BitComet recently cut a bit of software from itself that gave it speed, so its really no faster then normal Bittorrent. The fastest are uTorrent and Azureus. I personally use Azureus, just remember to remove your old versions of Java otherwise Azureus gets memory leaks Other then that Azureus is fast, multiple torrents and gives you more information then you'd know what to do that, plus it's Opensource Software.(the old versions are like 'Java 1.5 update 4', just remove these until only the newest update exists)
azureus.sourceforge.net