Caution: Maybe the longest wall of text in this forums history on something that could be summed up quite quickly. 
I've been following the discussion between ART vs Dalvik and for some reason it kind of fascinates me. I decided to give ART a try on my S5 (Sprint, U.S) after hearing that it speeds things up.
I do love the S5 for its many great traits, but as always with Samsung, they close to, if not completely destroy the experience with their atrocious software, vomit inducing bloatware, and overall business practices. They're like the big dumb "meathead" (no offense, meatheads), packing on all the muscle that they can, while the substance within that it works to sap so much of that power's potential. Just terribly inefficient. I'm a stickler for efficient performance, hence I've disabled and turned off just about everything in the S5 that I don't need (that friggin' Samsung allows) sped up animation transitions, so it's a lot faster than "stock", but you can imagine my love/hate relationship with the device and those its creators.
The S5 IS fast and slick, but it should be MORE fast and slick. The home button lag (even with S Voice turned off), the Multitask button lag, overall Touchwizz lag, stuttery graphics/motions every now and then, just shouldn't exist on such a brutally powerful piece of software.
So I heard that "ART" fixes some of this:
The Good: Firstly, I'll say that I was EXTREMELY impressed by how slick, fluid and refined it felt, the touch, the swiping, graphic changes, everything at least "seemed" noticeably more fluid and quick/responsive. It felt as close to an iOS/Apple device in software optimization related refinement that Android, and especially Samsung has gotten. It's very exciting to know that Google is working so hard in in my opinion, "finally" making Android really "feel" refined. The Multitask button got WAY faster in response, almost as instantaneous as the HTC One (M8), yes it still had that classic Samsung lag, but much less so (you couldn't drink an entire glass of something while waiting for your open Apps to appear).
The bad: It's very unstable and crude with Samsung/Touchwizz. Some Apps and Widgets had distorted icons (or went black), which would work itself out after I deleted then re-put them up on the home screen. The phone seemed to run hotter than usual, which makes sense as it was probably facing glitches constantly. Thus, battery drainage "seemed" to increase, which again makes sense as something that's so at odds with the phones software/skin would sap resources. Though I don't know if it would have "settled" down and gotten more stable and smooth if I kept it on for more days (only had it on for one day).
Polaris Office didn't work (I downloaded Google Office while I had it on). The phone took a long time and got extremely hot as it switched to ART mode (much less so to switch back). The memory got taken up a lot more (if you don't have an SD Card, beware). Private Mode didn't work (one of many reasons I switched back).
What got me to switch back, though, was when I was charging it, it didn't seem to recognize the USB charger for a little while. Then when it did, I used my phone to make a call, and minutes into it, it died. I've never had that happen as the charger always provides enough charge to let me use the phone at will even with 0% battery. For the record, part of this MAY have had to do with the cable not being firmly set into the wall charger, but the long recognition was at least definite.
Another thing that got me to switch back was how my phone app got super glitchy and was going crazy during my call (sensors somehow came on and it kept opening and closing). However, after switching back to Dalvik, I was getting those issues now with that! Which brings me to another issue: Some issues that ART introduced did sort of carry over into Dalvik. Such as that AND my system always having a "Software Update" icon on the upper left hand corner when I reboot the device (which never happened before switching to ART).
Another thing to mention is that although Apps launch faster with Art, they LOAD considerably slower, an issue many report. So you'll see it boot up very quick, but you'll wait longer than usual as it loads itself up.
Even the Android System seemed to continue to drain disproportionate (vs before) battery after switching back to Dalvik for a little while (settled itself out after a few charges), since ART started causing that problem as well.
Also, Touchwizz "failed" once, as did some other random processes, which surely had to do with what I at least believe seemed to be increased battery drainage.
.... WOW, that's a long story! Hopefully this adds some insight to anyone who's considering the switch, but afraid of the horror stories. Mine isn't nearly as bad (or good) as some stories that have bricked, etc. phones, but I will say that after experiencing it, I long to have it active on my phone again.... my experience has suffered since I now "know" how much smoother ART feels in the touch and responsiveness dept. Though it's just too flawed and quirky/clunky otherwise to try it again. I've heard people say that portions of the Camera app have crashed on them, therefore pictures didn't look as good, just not worth it yet, but can't wait until it's officially released.
I've been following the discussion between ART vs Dalvik and for some reason it kind of fascinates me. I decided to give ART a try on my S5 (Sprint, U.S) after hearing that it speeds things up.
I do love the S5 for its many great traits, but as always with Samsung, they close to, if not completely destroy the experience with their atrocious software, vomit inducing bloatware, and overall business practices. They're like the big dumb "meathead" (no offense, meatheads), packing on all the muscle that they can, while the substance within that it works to sap so much of that power's potential. Just terribly inefficient. I'm a stickler for efficient performance, hence I've disabled and turned off just about everything in the S5 that I don't need (that friggin' Samsung allows) sped up animation transitions, so it's a lot faster than "stock", but you can imagine my love/hate relationship with the device and those its creators.
The S5 IS fast and slick, but it should be MORE fast and slick. The home button lag (even with S Voice turned off), the Multitask button lag, overall Touchwizz lag, stuttery graphics/motions every now and then, just shouldn't exist on such a brutally powerful piece of software.
So I heard that "ART" fixes some of this:
The Good: Firstly, I'll say that I was EXTREMELY impressed by how slick, fluid and refined it felt, the touch, the swiping, graphic changes, everything at least "seemed" noticeably more fluid and quick/responsive. It felt as close to an iOS/Apple device in software optimization related refinement that Android, and especially Samsung has gotten. It's very exciting to know that Google is working so hard in in my opinion, "finally" making Android really "feel" refined. The Multitask button got WAY faster in response, almost as instantaneous as the HTC One (M8), yes it still had that classic Samsung lag, but much less so (you couldn't drink an entire glass of something while waiting for your open Apps to appear).
The bad: It's very unstable and crude with Samsung/Touchwizz. Some Apps and Widgets had distorted icons (or went black), which would work itself out after I deleted then re-put them up on the home screen. The phone seemed to run hotter than usual, which makes sense as it was probably facing glitches constantly. Thus, battery drainage "seemed" to increase, which again makes sense as something that's so at odds with the phones software/skin would sap resources. Though I don't know if it would have "settled" down and gotten more stable and smooth if I kept it on for more days (only had it on for one day).
Polaris Office didn't work (I downloaded Google Office while I had it on). The phone took a long time and got extremely hot as it switched to ART mode (much less so to switch back). The memory got taken up a lot more (if you don't have an SD Card, beware). Private Mode didn't work (one of many reasons I switched back).
What got me to switch back, though, was when I was charging it, it didn't seem to recognize the USB charger for a little while. Then when it did, I used my phone to make a call, and minutes into it, it died. I've never had that happen as the charger always provides enough charge to let me use the phone at will even with 0% battery. For the record, part of this MAY have had to do with the cable not being firmly set into the wall charger, but the long recognition was at least definite.
Another thing that got me to switch back was how my phone app got super glitchy and was going crazy during my call (sensors somehow came on and it kept opening and closing). However, after switching back to Dalvik, I was getting those issues now with that! Which brings me to another issue: Some issues that ART introduced did sort of carry over into Dalvik. Such as that AND my system always having a "Software Update" icon on the upper left hand corner when I reboot the device (which never happened before switching to ART).
Another thing to mention is that although Apps launch faster with Art, they LOAD considerably slower, an issue many report. So you'll see it boot up very quick, but you'll wait longer than usual as it loads itself up.
Even the Android System seemed to continue to drain disproportionate (vs before) battery after switching back to Dalvik for a little while (settled itself out after a few charges), since ART started causing that problem as well.
Also, Touchwizz "failed" once, as did some other random processes, which surely had to do with what I at least believe seemed to be increased battery drainage.
.... WOW, that's a long story! Hopefully this adds some insight to anyone who's considering the switch, but afraid of the horror stories. Mine isn't nearly as bad (or good) as some stories that have bricked, etc. phones, but I will say that after experiencing it, I long to have it active on my phone again.... my experience has suffered since I now "know" how much smoother ART feels in the touch and responsiveness dept. Though it's just too flawed and quirky/clunky otherwise to try it again. I've heard people say that portions of the Camera app have crashed on them, therefore pictures didn't look as good, just not worth it yet, but can't wait until it's officially released.
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