For the new cars, I'd NEVER pony up for the 330. The premium over the 320/325/etc. is way too much. BUT, in the used market, things work against the 330 owner. 330 prices are much closer to 325/320 prices.
For that reason, I'd search for the 330 version. The only way I'd buy a used 320 model is if I got it VERY cheap with the gap between the 320 and 330 being more than when it was new. That is unlikely, but could happen.
The other thing to consider is the car. A beat-on 330 is a loser compared to a pristine, cared-for 320 no matter the options and cache. This means some searching might be required. Teen driver in the home? I won't buy your car. Sorry to all the super-responsible parents, but I see WAY too many folks letting their teen beat the crap out of their $60K car/SUV.
But, what about a lease return? That's a bit more trouble, but can be a safe bet if you play your cards right. A very careful inspection (yes, even on warranty cars) can tell you lots about the PO and the treatment the car recieved. Premium lease-returns like BMW's often have service records and warranty-claim lists.