This seems to be a competitive market for all the carriers, which makes me lucky. Most years AT&T is rated the best, which is somewhat ironic since they aren't the best for me -- of course, most of the testing is done in the city. Verizon has been second most years, though T-Mobile has been competitive the last few years. As I said, I believe Verizon was in the process of doing network upgrades last year, which hurt their scores -- I'll be curious to see how the carriers do this year.
To give you an idea of how good we have it here, my first two speedtests with my T-Mobile Unlimited plan -- the first late last night (early this morning), the second at 11:35 am.
http://www.speedtest.net/iphone/1986115036.png
http://www.speedtest.net/iphone/1986681451.png