god of war 1
god of war 2
god of war chains of olympus

killzone 1
killzone liberation

im trying to play all the prequels before i play the sequels

You're not giving us a lot to work with. =P

But the first God of War game should be pretty cheap by now, so I'd suggest buying it, finishing it, then deciding if you should rent or buy the next two.

Rent them all.

Buy GoW! they are only like $18 to buy anyways and a rental is 11.29 at blocky atleast.

GoW - buy, KZ - rent.

Gamefly them all except the original Killzone. There's really little reason for you to play that at all outside of making you appreciate Killzone 2 ten times more.

Buy all of the God of War games, rent the Killzone games.

God of War II remains one of my favourite games of all time.

ok how long does it take to finish each 1 of those 5 games?

GOW buy

GOW and GOWII: 10-12 hours
GOW CoO: 5 hours
KZ: I dunno, didn't finish it ^^
Liberation: I dunno, didn't finish it (I think it's one of the most boring game I have on PSP!)