Finally got the Spigen ultra crystal screen protector for my Nexus 4. And I have phantom skinz ultra clear screen protector on my Note 2. Both have front/back screen protectors. Although, both are really close, IMO the winner is...
Phantom Skinz ultra clear screen protector!
1) Fingers glide much smoother than the Spigen. It was quite a noticeable difference to me. Although, I'd like to mention that the S-pen felt much smoother on the spigen than phantom skinz. Almost a little too slippery for my liking, though doubt I would notice much difference when using it.
2) This might have to do with the color of the device (black vs titanium grey), but while Spigen looks damm near invisible, with the phantom skinz, I could barely tell I have a screen protector on.
Some things I liked about Spigen:
1) Dry-install. I used to hate doing dry install, but this one was quite easy. I took my time, but the biggest advantage I see in dry install is if you get dust/link stuck underneath, you can easily lift up the Spigen screen protector and use Spigen's "special" dust/lint removal tape and reapply. I was able to get a perfect no bubble, no lint, no dirt install.
On the other hand Phantom skinz is a wet install. Biggest problem with this is you can't see the dust/link or air bubbles until after you install. I usually leave phone off for the night and in the morning I will unwrap the ceran wrap that I covered it with. Luckily my note 2 turned out great, but it wasn't as easy as installing like Spigen screen protector. Also, water can be bad if you aren't careful and let the phone dry long enough.
2) Ease of installation, again with dry install and a You tube tutorial video, I was able to install this with no problems in about 30 minutes. Aligning it was quite easy with the tape method I found on You Tube. The phantom skinz takes me a little longer (much longer if you count drying it overnight) due to water and covering it up with ceran wrap so I the screen protector doesn't lift and get air bubbles.
3) Cost. Technically they both are about the same price, but you can't buy one set of full body screen protector form phantom skinz, they come with 2 sets. Even though phantom skinz says it's a "internet special, BOGO free" it's really not if you compare it to other screen protectors and their prices.
**Update**
Thought I'd update this after using the Spigen screen protector for a little while more. I have to say it's a tough call between these two. After normal usage, I really don't notice that extra bit of drag on the Spigen protector. Fingers slide just as well as the phantom skinz. One thing that I noticed, is even after a couple days of letting it cure to my screen, I was still able to lift it up with scotch tape. If for some reason you have something sticky (like scotch tape sticky) on your finger and touch the screen, it may lift the screen protector up completely. This may be the downside to dry-install in general. Whereas phantom skinz is stuck on there unless you really try to get it off. I've also already made a scratch on the back side of the Spigen screen protector, no idea how that happened. No scratches so far on the phantom skinz (been using phantom skinz for about a month now).