It depends on what you want to do with the computer....in general:
The Athlon is a bit faster in many games and kicks the Pentiums butt in several games.
The Pentium is faster at encoding audio and video and doing several other none gaming applications like POVRAY and such.
For me it came down to the fact that although I do A LOT...and I mean a CRAPLOAD of video encoding ( I have a secondary puter I use like a tivo, and use my faster primary computer to re-encode the mpeg2 captures into mpeg 4 reducing the size to 1/3 the original). I can setup my encoding to run whne Im not using my system, sure it takes 1:45 to reencode a 1 hour show, but who cares Im not sitting there watching it. When Im playing a game, I need the computer to be as fast as possible right then.....so if you play games and arnt rendering an animated 3d render movie full time....its pretty clear IMHO what you should do.