For 451 Quests, they are still (as last I heard) selling Quest 2s. For 559 (26") Quest, they are selling Quest 3s. The major difference for the Quest 3 is they swapped out the suspension front fork for a fixed front fork.
As far as telling by looking, it's whether or not you see the suspension on the fork: This one has it. If you don't see the "black accordian" rubber below the headtube, then you have one without suspension.
I've had a Quest 2.0 for several months now. Bought it used for $1500, and I really enjoy it. I travel with it frequently. If you have any questions, you can e-mail me at jeffwittenfeld@comcast.net. I also have a Sofrider V2