There are four major carriers and a few minor carriers in the U.S. and all of them offer at least a few Android handsets. But it’s what they do with their handsets that differentiate them. Each carrier has their own pricing and coverage differences as well. I’m not covering those here.

The grade card:

T-Mobile: A-

Even though it is the smallest of the big four U.S. mobile carriers, T-Mobile has done more than any of the others for the Android platform. T-Mobile carried the G1, the first commercially available Android phone. It was also the only carrier to subsidize the Nexus One — the Google Phone.

T-Mobile is also pretty low key on installing their own apps. I even enjoyed the free Avatar showing they included with the Samsung Galaxy S Vibrant. They did have a stinker recently with their Charm effort, though I lay most of the blame for that phone on Motorola (MOT). The company’s upcoming G2 is more of the same, pure Google (GOOG) experience, but aside from that and their Vibrant, they don’t have any standout Android devices like…

Sprint: B+

It is hard to compete with Sprint’s two Android heavy hitters, the EVO and Epic 4G. Both of those phones can go up against anything Verizon has to offer and yet they are left fairly untouched by the carrier.

Sure, Sprint (S) includes irremovable apps like NASCAR, SprintTV and Sprint Navigation, but overall, the apps are pretty harmless. Sprint also gets points for being the first carrier to update their phone (EVO) to Android 2.2, though they did balk at carrying the Nexus One. They also don’t prevent side-loading of apps like…

AT&T: C

AT&T (T) gets third place for showing up, which is a good representation of the company’s overall attitude toward Android. They have yet to offer a phone with Froyo, the only carrier with this unwelcome distinction. They have two great pieces of hardware, the Captivate and the Aria, but you’ll have to find them on a wall of mediocrity at the AT&T store. They also proudly carry the Dell Streak and Sony Xperia, which are both sitting on Android 1.6, sadly.

AT&T also doesn’t allow side-loading of apps, like the other carriers. AT&T was the first to try to supplant the Google search experience by putting Yahoo Search as a default option on their Backflip phone. That move really benefited their customers.

That being said, they don’t really mess with the Android experience in a harsh way, which brings us to Verizon.

Verizon: C-

Verizon (VZ) might have the strongest Android lineup of any carrier.  The Droid family is also undoubtedly the best-selling line of Android phones, and no single phone has done more for the Android cause than the original Droid, which was an instant marketing hit. Verizon even updates their phones as fast as anyone, with the whole Droid lineup now boasting Froyo. Verizon also aggressively markets Android

But in exchange for their popularity, the carrier has begun to mess with the experience at the customers’ expense. Their Verizon Fascinate now comes with Google’s search removed (and locked to stay that way), replaced with Microsoft’s Bing. Verizon says more phones are coming with this “feature.”

To top it off, Verizon is opening a competing Android market that will try to lure developers away from Google’s Global Market. The carrier has also cut deals with Microsoft and Skype to gain exclusive access to their apps, meaning that they can’t be used on other carriers’ Android phones.

Overall

It feels a bit like we are at a point where the carriers — well, Verizon mostly — are starting to move in on the Android experience. It will be interesting to see what, if anything, Google does in upcoming releases of Android to stave off this encroachment. If you want an Android experience as Google intended, your options pretty much begin and end with T-Mobile, though you probably won’t mind the light window dressing Sprint gives its Android devices.

See also: Android hardware report card here.