Define "best" first... heh...
I've currently access to 3 quite fine computers, where two of them are currently running as servers. Usually, when one's comparing one computer with another, one checks which of them have higher scores in various benchmarking programs. In such a case, I would pull a few components from each computer as all of them have something better than the others...
For graphic card benchmarks, I'm kind of out of the game... well, I have a quite nice card and it's price-worthy... but it's a little bit "last year".
For overall system performance, I would simply pull out the hardware RAID array out of one of my servers, push it into my main computer... configure it for RAID-0 with the four 500 GB drives which gives it a superior performance in the HD-benchmarks (okay... it's probably beaten by two Raptor disks... but those are horribly expensive!).
To further increase performance in an overall system benchmark, one would likely try to overclock one's CPU (as those tend to be the primary thing that gets benchmarked...). For the moment, I have the Q6600 running at 3.0 GHz on each of the four cores in a dead stable state (actually running it at decreased voltage... rather unusual!). For benchmarking purpose, I'm fairly certain that I could push it up to about 3.4 GHz which is hard to beat without paying lots of money on the high end quad core processors. Oh... and with a better stepping, it should be able to get to about 3.8... not that I recommend it to anyone running it 24/7.
So all in all, it comes down to... "best when? and best in what way?" :p
