Vanilla or Modded TTT?

Modded.
Vanilla has been overplayed far too much unless you're bringing someone new into the game or playing around with some friends.
A game with new things is always better than the same old thing. If there are mods, it usually means that the server's had a ton of effort put into it and because of that, it's likely that there'll be more active moderators and admins that can keep the community in check and fun for everyone.