Speaking from a decade of experience, going to a Mega-Church is like going out to a country fair; you rarely see the same people twice, you shake hands and exchange pleasantries woth folks you never see again...and you wind up leaving not quite satisfied as a result (then there are the folks who smile, waive, run around and pretend they know everyone - spare me)....my own experiences with small churches have also been more positive....if I were still in San Antonio I'd probably still be attending one....
I've attended large churches and attended small ones. Each has their strengths and each their weaknesses. The large ones can become too impersonal. The small ones can become too personal. The large ones can get wayward because they become too corporate or political. The small ones can get wayward because too few are depended upon to do too much. In the large ones, I found the real fellowship and accountability came in being part of a weekly Bible study. That's probably where I learned the most - in a "church" within the church.