SGV. I was mostly satisfied with Cingular back in the day, but since switching to T-Mo in 2004 I've been 100% happy with my voice plan. So I'd more regret losing the cushy grandfathered voice than regretful of AT&T... still going from 1000any/unlimited night and weekend to ~700 any minutes on the AT&T is quite a big difference... even if I average between 400 and 600 minutes a month.
About the only thing that could keep me T-Mo at this point is magically getting $5.99 unlimited T-zones/EDGE turned back on. Maybe the new $10 unlimited plan... maybe, but the 3G draw is pretty good as you noted,e specially since I can rope my wife in on a family plan.