Well, after all the problems with Transmission and popular trackers like OiNK and Demonoid I decided to try something else. I tried out Tribler, but it wasn't that good, so after snooping around the Ubuntu forums I found about this relatively new client called qBittorrent. At first I refused to use it, as I don't like running Qt apps under Gnome, but after searching some more, and not finding anything better I decided to go for it.
The client is way better than anything I've used before. It even has an inbuilt torrent search plugin, like the famous uTorrent on windows. It also has all the major features you may need/want from a mature client.
The good news is that it is actively developed, it has a very nice and fresh look, and there's official Ubuntu and Debian packages on the download page and last time I checked it was in the repositories. That's a lot to say, because we now have official support from the qBittorrent team when packages don't work, etc.
All in all, its the best client I've used so far. Try it out!