I favor the 39-2; mine is the nickel version. Rides very well in an old black leather Uncle Roy's Pancake holster. I have to admit I rarely carry it anymore, usually my Model 38 resides in a Mika pocket holster.
Chris, aside from the 3rd generation having a firing pin safety the hammer and trigger bar configuration was also changed on the 3rd generation guns. The 1st and 2nd gens have a "safety notch" on the hammer. The 3rd generation guns do not. Also, the trigger spring tunnel is a better (reliability) shape and the slide lock configuration is different as well. There may be other changes of which I'm not aware.
S&W Single stacks. I've always loved them, but SW never made what I really wanted. A single stack, with rounded trigger guard, an alloy frame, full sized. Had a 639, but thats just to heavy for a single stack nine. Not that it didn't shoot well, and feel good in the hand, I just wanted something larger like my 3913. I sqrewed up years ago not getting a 909 when they first came out. I have since remedied myself of this issue. Now since I'm a lefty, I'm thinking about finding a full sized 3rd gen slide and barrel with ambi safety. I know it will be a FrankenSmith, but I have tried the slide off my 5904, and she works very well, and looks cool too!