I have the 4s and iOS6 and am pretty happy, I also have friends with the 5 and they're happy.
Whichever phone you buy from teh current market you'll have some great features and some annoyances, the Smartphone market has come a long way but is no where near perfection yet.
Android - Really pushes the envelope on what you can do but the phones are only compatible with the current latest greatest firmware version for 6 months then you need new hardware in order to take advantage of the new features available.
iOS - Reliable interface, does most things pretty well, has a few dodgy things like the new maps (I'm not an android user but surely they aren't flawless?!?) your phone will most liekly be able to use new firmware and features for a good 2-3 years (3Gs case in point) and the app store is sooo much better than google marketplace
Windows Phone - Let's face it, this isn't considered to be a major contender currently but is coming along pretty well, I know a couple of people with them that absolutely love them, don't be suprised if they're a force to reckon with in a year or two.
The way I see it, if you're a bit of a tech head and can work around problems then Android will probably work well for you, if you're not overly confident with technology and you want something simple and consistent to use, iOS is the choice to go with. My grandad is 90 and never used a computer but has just got an iPad and is used to it already.
Hardware wise, the latest of any of the major smartphone manufacturers will do you proud, Samsung, Apple, HTC, etc, they're all making cutting edge technology.
Despite everyone protesting I'll probably stick with the iPhone for a while, it works well enough for me, integrates with my macbook and my wife's iPhone, I have apple TV at home and it's cool being able to instantly put my photos or music onto the bigscreen.