I've been following iOS since the first iPhone and have tried Android since Gingerbread with the Motorola Droid. After flip flopping back and forth trying both platforms one at a time, I'm finally test drove both for several weeks and I'm writing up my opinions on both in this post. This is just my two cents so that I don't have to constantly repeat it to friends, coworkers or strangers on this particular subject.
Apple iPhone 5 (Verizon) and LG Nexus 4 (T-mobile)
The latest iPhone is pretty much worth every praise that has been thrown at it so far. Everything from build quality, hardware selection and how it operates is a step up from the previous generation 4/4S. It's also finally has LTE which makes it on par with all the Android phones out there. Once you've tried LTE, there really is no substitute. In a non oversold/saturated area, I'd take LTE over some random WiFi connection. So yes, it's that good.
With all of this comes the ecosystem backing iOS and it's still the best out there. This is just my personal opinion but third party offerings still looks better or is only available on iOS for the most part. This gap is narrowing somewhat but there is still a noticeable difference.
Sadly, it's not all positives and good feels. The first party offerings are slipping. Apple Maps works and hasn't navigated me into a lake (yet) but the POI and overall polish feels more like a beta product than Siri is. The emphasis on skeuomorphic design really isn't my thing nor is the lack of consistency in presentation. An example of this is how the top bar goes "blue" in certain apps/menus (Calendars and Settings) whereas it stays black for the most part in everything else. That and ... iOS really feels dated. There, I said it.
That whole disconnect between hardware and software will hopefully be resolved with the change up in management but I don't believe it's going to make much of a difference till iOS 8.
And here is the latest Nexus device. After having had a chance to try out a Nexus S and having owned a Galaxy Nexus, build quality wise, this is the best so far. It feels solid even if I'm not a huge fan of the glass back. I would've thought manufacturers learned from Apple's mistake with glass backs on the 4/4S but it does add a quality feel.
Hardware wise, it's also not left wanting. I personally thought the Galaxy Nexus felt very part bin-ish and that Samsung cheaped out to make sure it didn't compete with it's other devices. This time around, it has a great processor, up to date camera sensor and a great screen. The colors doesn't pop like it does on an AMOLED screen but it's definitely seems sharper and cleaner overall.
Where it truly shines is under the hood and all of the first party/Google applications. Between Gmail which FINALLY has pinch to zoom to Google Now which feels more fluid to use than Siri, Android has finally matured with Jelly Bean 4.2 (IMHO). Plus, it's pushing the boundaries with Photo Sphere and other add-ons which is sure to come as a part of the Nexus program.
Now, the one huge omission is the lack of LTE. Yes, you can enable LTE via a test menu but it really doesn't apply to me since I don't live in an AWS LTE area (yet). Admittely, HSPA+ isn't as bad as I thought it would be. I've seen speeds up to 20mbps down and 2mbps up on T-mobile. Still no where near the 30/15+ on Verizon LTE but for the most part, it's usable. If anything, the truly noticeable difference is the latency especially if you're not stationary. During my testing, Verizon LTE seems to be less affected by movement/travel unlike HSPA+. YMMV but HSPA+ feels like "stop, stop, stop, burst" and LTE is more akin to "blam - no wait (unless you swing back to 3G)". So if anything, this hurts my overall opinion of the Nexus.
So the big question is ... which one did I choose?
Right now, I prefer the Nexus 4.
Even with the lack of LTE, I seem to grab the Nexus 4 more than the iPhone 5 and here are my reasons why.
I really thought that a 4" screen smartphone would be the best compromise size between usability and battery life. But I'm going to admit, besides the battery life (which the iPhone is amazing with in a good signal area), pushing it to 4" made it more than a handful. I personally can't one hand operate the device with ease like I did the iPhone 4/4S. So if I need to use two hands, I might as well pick the device with the larger screen since it's easier on the eyes.
Google Now is also a feature that I'm beginning to use and rely on more. Plus, I find myself navigating through Android faster than I do with iOS now. I can turn off/turn on features with less steps than iOS.
Carrier choice also plays a factor into all of this. I realize that it's a combination of device and network but you can enable WiFi tethering on the Nexus 4 without any additional fees on T-mobile. It's not a feature I use often but it's convenient to have regardless. That and the fact that I don't believe I should be charged for said feature.
With all that said, I don't believe you can go wrong with an iPhone. It's available via LTE on almost every carrier besides T-mobile right now and it's a great device. It's not like you can pick up a Nexus 4 with any amount of ease right now since it's sold out everywhere unless you want to spend a premium and get it through auction sites.
But if you're in an area that T-mobile HSPA+ is actually decent, it is a great alternative. Especially if you're not a heavy voice user since I'm on the 100 minute/unlimited text/5GB of "Faux G/HSPA+" data for $33 after tax. That is kind of hard to beat.