I recently met a guy who works for Bit Torrent, and he told me that with the current release, almost all of the other torrent clients out there are using identical code to Bit Torrent, so there's very little difference.
Personally, I use Transmission. That's Mac only, however. If you don't have a Mac, use uTorrent.
uTorrent. It's light and very simple to use.
http://www.utorrent.com/
All torrent clients work on the same P2P network so there's no difference in the downloading and uploading speed regardless of what torrent client you are using. The only difference is the amount of memory and CPU time that they use on your computer when it is running.
By the way, isohunt is not a torrent client. It's a torrent site.