I have a couple of favorites for different situations.
For live my favorite is a 6.5X14 Craviotto Unlimited. The drum is fat and very warm sounding, it just sits perfectly in the mix. This one goes everywhere with me!
For recording, I really like my 6.5X14 Ludwig Black Beauty. I don't know what it is about that drum, but NOTHING beats it in the studio. I have brought many snares into studios to record, but the Black Beauty is on EVERY album/cd I have recorded.
It's not my favorite, but my Ludwig Classic Maple snare is really a gem, especially for the price. If I only had a couple hundred bucks with which to buy a snare, I would definitely get a newish Ludwig Classic Maple. They sound good in just about any environment, they are sensitive, and they are fairly cheap.