What size?
the 2nd and 3rd 8gb are the same hardware wise - one comes with 3.0 and the other doesn't. That is a $5 to upgrade too.
The 32 contains the newer hardware, and comes with the headphones with Mic ($30 to buy the apple ones later).
I own a 3rd gen 32 and a 2nd gen 8gb. I will be buying another 3rd gen 32 - it really is faster. I figure too that the newer games that will be coming out will push the hardware limits (they have the Touch instead of a DS, so a lot of games). This way i future proof it more.
But between the 8gb? I'd buy a 2nd gen refurb from Apple.com (well, i'd actually go for the 16gb).