I've had a Galaxy Nexus sitting next to my iPhone 4S for about two weeks now, and I keep picking one up, using it for an hour, getting annoyed, and switching to the other. So I figure it's time to actually write down what I think instead of just complaining to my roommate about it at midnight.
Quick disclosure: my Galaxy Nexus is the unlocked GSM one, not a Verizon unit, because the Verizon version has been delayed so many times I honestly lost track. Something about a patent dispute over how the notification swipe works, apparently. Anyway, I've been running it on AT&T's HSPA+ network, which is fine but obviously not the LTE experience Verizon folks will eventually get.
The screen is the first thing you notice
The Nexus has this 4.65 inch curved glass display and it is genuinely gorgeous in a way photos don't capture. The iPhone 4S's 3.5 inch Retina screen is sharper pixel for pixel, no argument there, but it feels small now in a way it didn't two weeks ago. That's the real danger of using a big-screen Android phone for any length of time — you go back to the 4S and your thumb keeps hitting the wrong thing because everything's more cramped. I didn't expect that to bother me as much as it does.
Android 4.0 actually feels finished
I want to be fair here because I've used Android since the Nexus One and a lot of it was rough. Ice Cream Sandwich is the first version where I'd hand it to my mom without a disclaimer. The soft keys instead of physical buttons took about a day to get used to, and the font (Roboto) is a big improvement over whatever ugly default Android was using before. App switching is smooth, the camera app doesn't feel like an afterthought anymore, and Face Unlock is a fun party trick that fails constantly in bad lighting and is basically useless for actual security.
Siri, meanwhile, is the headline feature of the 4S and it's a mixed bag for me. It's great for setting timers while I'm cooking and for "text my sister I'm running late." It's bad at anything with any ambiguity, and it still says "I can't take dictation right now" way more often than Apple's commercials would have you believe. My favorite bit is asking it what phone is the best phone, which gives you a canned joke answer — cute once, not cute the fortieth time.
Battery life: neither one is good
Let's not pretend either phone impressed me here. The iPhone 4S got noticeably worse battery life after the initial software update that a lot of people (including me) installed to try to fix it, and I'm still charging it around 4pm most days if I've used it much. The Galaxy Nexus is about the same, maybe slightly worse, though the bigger screen makes that more forgivable. If you're the kind of person who carries a charger in your bag, neither of these phones is going to change your habits.
The Carrier IQ thing has me spooked, a little
I'll be honest, the whole Carrier IQ business that blew up a couple weeks ago has made me more paranoid about both these phones than I'd like to admit, even though nobody's proven either device is doing anything with it right now that I use daily. It's less a Galaxy Nexus vs iPhone thing and more a general "wait, what exactly is running on my phone" thing. Worth keeping an eye on going into next year.
So which one
If you'd asked me the week the 4S came out, right after Steve Jobs passed, I'd have said iPhone, easy, no contest. Two weeks with the Nexus has actually moved me. The hardware feels more ambitious, the software finally doesn't feel like a hobbyist project, and that screen has spoiled me. But the app selection on iOS is still deeper for the stuff I actually use daily. My banking app, a couple of photo editing apps I like, and that matters more day to day than I expected it to.
Right now the Nexus is in my pocket and the 4S is charging on my desk. Ask me again in a month and I might have flipped back. That's kind of where Android and iOS both are at the end of 2011, honestly. Close enough that it comes down to which annoyances you'd rather live with.