I'm an AF staff psychiatrist, a few yrs out of residency. The 2 AD training programs have some differences. The San Antonio program is at Wilford Hall, which despite cutbacks in services there remains the flagship AF hospital. Networking, etc might be a bit easier there. If you have any interest in getting flight surgeon wings (a good idea if you plan on staying in the AF long term), the San Antonio program used to let its 4th year residents do the 6 week aerospace medicine primary course as an elective which could not be done at WP. However, in 2011, it looks like the School of aerospace medicine will be leaving San Antonio (ironically for Wright-Patt) so that advantage could switch. WP is a more community-based program and emphasizes psychotherapy to a degree more than San Antonio (probably more than most psych residencies nationwide), so you may want to take that into account.
Overall, you'll get fine training at either. You'll be competent and pass your boards with the training you get at both of these sites. How high you "soar" beyond that level really depends a lot more on the kind of student/doc you are than on the program you train at.