Personally I find Azureus like running a foot race with work boots. I think it's because it's fully coded in Java, which personally I have always found sort of sluggish, despite its flexibility (Keep in mind I don't know jack about programming).
That said, Transmission is my #1. I wish it had the ability to download only certain files from a torrent. That's my only complaint really. Transmission is fast as hell and uses a really small memory footprint.
I've also used BitRocket which I have found to be very likely the most unstable program I've ever used on a Mac. It crashes every time I add a new torrent without having it running first, it crashes when I am editing the properties of a torrent, it crashes on startup sometimes. It's a great program, but I just wish it were more stable.
So, for me the answer is Transmission. I think you will find Transmission to be what you're looking for as well.