stock is always the fastest, becuase its built into android. any other launcher is just an app sitting on top of the stock launcher thats taking up memory.
however, I use LauncherPro SenseUI (paid version) becuase its FAST, has the full sense theme(which i like) and is based on launcher pro, so it works great.
I also have a home switcher and move between that and MetroUI Pro which is a Windows Phone 7 launcher. its also very well done with a lot of options that arent in the free version. I really like this launcher, Its my default most of the time. except when i need to prove to another android user that the phone is actually running android haha,