I have only experience with playing TTT on private Servers. And I really thing it is a lot of fun playing in a group of people you know. I never really enjoyed playing it on public servers. However since I know some people that own the game, that wasn't a problem. What really annoys me is setting up one of those private servers, until you have a decent experience. There are always things that could be better with so many mods out there. And even hosting a server on the internet was a real hassle. Probably should wait for S&box and hope they improve the "server hosting" issue. I suspect it will be pretty similar and have a much larger actively playing community, since GMod is already pretty old.