I greatly preferred the New Adventures revamp. I thought the animation looked a lot better, and it was consistently good as well. The original B:tAS had a lot of different companies working on it and some looked good but a lot looked absolutely terrible.
Plus, Batman looked a lot more bad ass with his blacker design than the old blue/yellow one.
As for the shows in general, Justice League Unlimited and Superman were the best. I find Batman had a lot of good episodes but also a lot of truly terrible ones as well; a poor good to bad ratio. Plus, it was just so amazing to see an animated Superman flying around and punching people.
Batman Beyond I found extremely uninteresting (though the Joker movie was amazing).