But I'd like to know which Linux has an appreciable performance on 64 bit processors with of course, lesser complexities involved.
They're all fairly simple to use, and the performance should be quite similar. If you're thinking "which will run program xyz fastest", then that depends on many different factors - the Desktop Environment for example (KDE and Gnome being the two biggest) or the daemons which are running in the background.
If you can tell us what you want to run on the system, we can possibly help you, but there shouldn't be much difference on any modern processor.
If you don't want to use Linux for a specific type of program but for general usage, I'd recommend to download the
LiveCDs of all three (
Ubuntu,
Fedora,
openSUSE) and just test them without installing. Decide, which you like most and then put it on your drive!
Oh, of course the systems won't be as fast from LiveCD as they will be when installed. So don't worry about that.
Greetings,
Nepomuk