Definitely use each carrier's trial period to determine if their service works for your needs. Even if your home is listed as being in a strong coverage area, perhaps the indoor service at home and/or work aren't up to par. This is always trial and error.
That said, the Sprint plans are usually a bit cheaper, and with the Sprint version of the Touch Pro 2, you would have a really nice international roaming ability too since it has a quad-band GSM radio in addition to CDMA/EVDO for Sprint in the states. I believe the Sprint version ships with 6.1, so you'd have to look into the availability of an upgrade to 6.5 (one would think this would be available soon if not already). You could find out more of the perhaps less obvious differences at Howardforums.com. There is usually some degree of bloat on ATT phones that can often be removed by flashing to a custom ROM.
I am going to purchase the HTC smartphone / WinMo 6.5 Are there differences between the AT&T and the Sprint versions? Any recommendations as to which carrier to use?