It's not the frequency of a network that matters, it's how it's put together. AT&T's 3G network in Austin for a long time was 1900mhz WCDMA, very similar to Sprint's 1900mhz CDMA network. Difference is, the 3G antennas for AT&T were put on towers that were designed and spaced for 850mhz 2G. The results were a disaster for 3G coverage in Austin. Sprint, however, has always had a 1900mhz system in Austin, and it works fantastic.
T-Mobile is even better off, their 2G is on 1900mhz, and their 3G is on 1700mhz. They should have overlapping coverage if they set it up right.
As for frequency, I've always been told that lower frequencies carry further and penetrate better.... but who knows. Even the Cellular companies themselves, esp AT&T, touted the building penetration abilities of their 850mhz network. And in my practice with AT&T's 1900 3G vs 850mhz 3G, the lower frequencies definitely had better reception indoors.... but maybe that was tower distance... Also, even if a 1900mhz signal can penetrate buildings better, it's rendered useless if the signal can't propagate as well as 850 and is very weak when it makes it to the building in the first place. It's probably best to not think of propagation and penetration separately. You don't get the right outcome.