When it comes down to it, I purchase my system based on the games.
The Xbox had how many great games? (that were only on Xbox) Like 5? (Halo, Halo 2, Star Wars:Nights, PGR2, Fable).
The PS2 had FFX, FFXII, GT3 & 4, Guitar Hero 1 & 2, GTA Vice City & San Andreas (yes they came out on the Xbox, but they were on the PS2 long before), Metal Gear Solid 2 & 3, God of War, Shadow of the Colossus, Tekken 4 & 5, Virtua Fighter 4, Kingdom Hearts 1 & 2, Resident Evil 4, Winning Eleven Soccer, Katamari... Plus you can play all the great original PSX games (Final Fantasy VII anyone?)
http://www.filibustercartoons.com/games.htm has a compiled list of the greatest games ever made according to various magazines. PS2 has 5 titles on the list, the Xbox has only 1.