The best smartphones on every carrier: a more succinct take
Given the hubbub in the comments section of Chris Ziegler's article about the apparent illogicality of his choices, I wanted to offer my take since I just e-mailed a friend with advice on this very topic last week. I certainly don't think my opinion is any more correct, but simply more streamlined.
The key assumption is that the reader is equally satisfied with iOS and Android. Vastly preferring one ecosystem over the other makes the choice for you, which renders the point of a "best smartphone guide" moot. A Verge commenter once wrote, "iOS is what Apple wants it to be and Android is, for better or worse, what you want it to be." I largely agree with this assertion - particularly with the implications regarding out-of-the-box performance and customizability.
AT&T: 1a. Samsung Galaxy S III 1b. HTC One X 3. iPhone 4S
Verizon: 1. Samsung Galaxy S III 2a. iPhone 4S 2b. Samsung Galaxy Nexus
Despite their differences in LTE deployment, both carriers have similar rankings. The main issue is that I can't possibly recommend a commitment to two years without LTE. Most urban areas in the US will have LTE (both Verizon and AT&T) at some point in the next two years, so a lack of LTE support is a handicap that's too big for the 4S to overcome - especially when you consider the superior specs on the SGS3.
SGS3 vs. 1X is a toss-up. I've given the SGS3 the edge because of the multitasking and wi-fi issues that have come up with the 1X, and because TouchWiz seems to be less obtrusive than Sense. A stock Android ROM might push the 1X and its superior display over the top; again, the difference between these two phones is mostly negligible.
Verizon lacks a second high-end Android device, so the 4S just beats out the GNex by virtue of a better display and a much better camera. Also, CDMA Nexus devices don't get the prompt Android upgrades that their GSM counterparts do. Nevertheless, the lack of LTE keeps the 4S from approaching the top spot.
Sprint: 1a. Samsung Galaxy SIII 1b. HTC Evo 4G LTE 1c. iPhone 4S
This is the biggest toss-up of all four carriers, because Sprint's LTE network hasn't even rolled out yet. The iPhone's biggest disadvantage is thus nullified. Again, I've broken the tie by favoring the devices with LTE support, as Sprint should have solid LTE coverage some time in the next two years. The SGS3 and Evo also have HD Voice support, a nice feature once Sprint launches it at the end of the year. I recently opted for the Evo over the SGS3 (because it came out earlier, and for the better display), but right now the 4S is just as good of a purchase.
T-Mobile: 1. Samsung Galaxy S III
The clear winner if you want a subsidized device and don't mind signing a contract. But that excludes the best budget option. . .
Best value: Unlocked Samsung Galaxy Nexus with T-Mobile's $30/month plan
At $399 off-contract, the GNex on this plan is easily the best bang for your buck. You'd be hard-pressed to beat the $759 (plus taxes) over 24 months, and HSPA+ provides a solid, if slightly inferior, alternative to LTE. You can also be confident of a prompt update to Android 4.1. For anyone on a tight budget who wants a full-featured smartphone, this is the way to go.
Final notes: The Lumia 900 comes in at #4 for AT&T, but the lack of a Windows Phone 8 update really hinders its "future-proofness", especially when iOS6 and Jelly Bean come out. Needless to say, these rankings will change when the new iPhone launches in October - readers who strongly prefer iOS should really wait until then to buy a new phone.