I'm a big fan of Tuwunel. Run Synapse myself since I've had a server running for about 7 years now, but if I had to start over, Tuwunel all the way.

There's also Continuwuity, which I think is more popular, but I don't fully understand the difference. I think it's a community split issue? As someone who maintains a client, Tuwunel seems to match the spec better, but I'm sure folks have better reasons to pick one over the other.