During the season I usually play either ProV1x's or Srixon Z-Star Tour Yellows.
I did try the TaylorMade (a) ball while down in Florida a few weeks ago and was surprised with both how well it held up and the overall performance. Definitely a decent ball.
During the late fall/winter months I'll play just about anything that hasn't been beaten to death already.
I generally buy my balls at my club's pro shop... primarily because I'm cashing in pro shop credit every few months and balls or gloves are always a good investment. And I like supporting my club, which helps keep my dues down in the long run. 🙂