I've never shot a QA although I've fired a few rounds from a Glock. I think the heavy DA pull on the AS makes it a safe gun to carry with a round in the chamber and ready to rock. The SA trigger for follow ups I'm not so sure about. I've fired a few K rounds through my gun and about 5 times the SA trigger was lighter than expected as if it hadn't fully reset. I really wouldn't want that to happen during a gun fight. I suspect that the QA trigger is easier to deal with during a stress full situation. For range shooting, well, get whatever you like best. You'll find people here that say they shoot more accurately with the QA than SA trigger on the AS. And the other way around. For defensive purposes I'm starting to lean towards a QA/LEM type trigger. Factor in how much time you can spend doing realistic drills. The QA is probably easier to be 'good' at with less training.
As far as ammo goes, price should only be a consideration for range shooting. Worry about controlability and damage potential when choosing a caliber for a defensive gun. If you can't control a 40, get the 9. Missed rounds do no damage at all
Decide if you'd rather have more rounds with less power than fewer rounds with more power (tough call). When I bought mine I was in CA so it was easy to go with the 40. Now I'm in CT (well, next week) and I see a high capacity 9 in my future
Oh, also consider where you may fire your gun in anger. If it's at home you may benefit from less noise of the 9. Outside it doesn't matter much. In other words, don't use a 44 Magnum to shoot a burglar in your house, you'll be deaf