Well if you can find a 20gig or 60gig one try to purchase that; since they include the PS2 hardware. If not, then go with the 80gig model.; since it can at least handle the PS2 emulation. The 20 and 60 models, despite having the hardwarem can also do the emulation playing too.
The emulation play has its advantages sometimes over using the available ps2 hardware. Like display scaling for high-definition TVs. Or some people claim using the PS3 hardware removes some lag in some games (I've heard claims that God of War2 runs smoother on a PS3's emulation play than on an actual PS2).
Or if you are gonna keep your old PS2, since you backup your PS2 games like me, then really it does not matter which you choose. Since the PS2 you've grown to love will still be with you.
