My thoughts after owning a Note 4 for almost two months and the Nexus 6 for about a month.
I love the stock experience more in tasks such as app opening and switching and text scrolling. The Note 4 text scrolling looks like it skips frames so I can't scroll and read headers or my twitter feed at the same time. I have to scroll, stop, and then read. It really hurts my eyes after doing this awhile. The Nexus 6, on the other hand, is very smooth and allows me to scroll and read simultaneously. I can read my rss feed, use other apps and consume media, then come back to the rss app hours later and I can read where I left off. I rarely use more than 1.5GB while the Note 4's ram is almost always maxes out to the point where I have to start over and find where I left off when I switch to that same rss app hours later.
Overall I have a smoother experience using the Nexus 6. The UI is so much better than TouchWiz. The system settings on the Note 4 is a mess and why do some apps need to hide the status bar like the calculator app? So not necessary. It makes me cringe when the Note 4 lags half a second when I press the overview button.Why is my year old Nexus 5(still on KitKat) more smooth and responsive than the ultra powerful Note 4 and, to an extent, the Nexus 6? Also try scrolling through a Hangouts message when it's on the bottom of a multi window session with SwiftKey. It's a buggy mess since the keyboard pops up every time scroll up. Out of all the software kitchen sink features the Note 4 offers I feel only the S-pen done well.
The radios on the Nexus 6 is better than the Note 4 by a lot. And what I mean by "a lot" I mean that I get a good signal and able to stream on the Nexus 6 at a good distance from the WiFi router while it stutters or I spend several minutes staring at that loading circle on the Note 4. At times I would get WiFi signal on my Nexus 6 while my Note 4 reverts to LTE because it can't get the WiFi signal. Sometimes I intermittently lose WiFi signal from the Note 4 while the Nexus 6 is able to hold it and at a farther distance. Downloading files and loading Web pages takes longer on the Note 4. I hardly feel you have to wait for something to fully load when I use the Nexus 6. Just today I compared loading a news article on both phones and I was able to go through all 9 pages on the Nexus 6 while I'm stuck loading page 4 on the Note(4). Mobile Chrome still sucks and I find the stock browser on the Note 4 scrolls smoother.
The camera on the Note 4 blows the Nexus 6's camera out the water(especially in low light situations) . One thing that makes the Note 4 camera terrible is that of you take a picture in low light and the subject is in motion even slightly, the picture comes out blurry. Multiple people on this forums have also commented on this problem.
Say what they want about Samsung bloat(I hate how they include Facebook and Instagram as system apps) but I get 45 minutes to a little over an hour more on screen time on the Note. Also the Note 4 has excellent stand by battery consumption compared to the Nexus 6. I think Google made stock Android ping Google Play Services a bit too much or something. Even when rooted Greenified the Nexus 6 wakes up way too much compared to my stock Note 4. The fingerprint scanner is nice and works very well but I prefer using the trusted device feature on Lollipop to unlock my phone.
Since you get 50% off any accessory under $50 when you register your Note 4, I was able to get an extra battery and charger kit for only $22. The fingerprint scanner is excellent and I rarely have to scan more than once to get to my home screen. The display is better but not by that much. Auto brightness is much better to me than the iOS copy cat adaptive display on the N6. I have to fiddle with the brightness settings on the Nexus 6 several times a day while I only need to manually change the brightness on the Note 4 once when I'm reading in bed at night. Since the Note 4 is still on KitKat I get the notification ticker(except for phone calls) instead of the obtrusive and annoying banner ios notification banner on the Nexus 6. I sure hope Samsung keeps the ticker when they update the Note 4 to Lollipop instead of using the stock notification.
Overall I feel the compromises I make in using the Nexus 6 is carrying it around while on the Note 4 I have to change the way I use a phone and have more patience in doing it. So far I feel I'd rather have a better experience than tolerating and being able to tolerate how I use a phone for a longer time. Although with that said, when I use the Note 4 as my daily driver I think I would keep this phone if I had to get rid of one and feel the same way when I use my Nexus 6.