I voted for azureus 2.5 although I'm using 3 with classic interface.
I tried using uTorrent after azureus had reset its settings :'(, but i dont like not being able to see the seeding and leeching torrents on separate parts of the screen at the same time.
I switched back to azureus after two weeks and I'm pretty satisfied with it.
I can't deny it feels much slower, but after you lower the Gui update time, the cpu usage also drops a bit. It stays around 3%. Even with a lot of seeding torrents and a week of uptime I still don't notice any performance hits.
Plus I'm a big fan of all the configuration settings