3leggeddog,
Generally speaking, any S&W pistol with a 4-digit model number (3913, 5906, 4006, 4506, etc.) is a S&W 3rd Generation pistol.
The most common models - and therefore the easiest to find on the used market - are the 5906 (the full-size 9mm) and the 4006 (the full-size 40 S&W model). These two models were the most popular with law enforcement agencies so there are more available as used guns.
However, S&W made an almost bewildering array of models within the 3rd Generation line, and that is what keeps us collectors happy.
Let's take the full size 9mm as an example. The base model (and the flagship pistol in the 3rd Generation linup) was the 5906. Probably more 5906s were produced than any other 3rd Generation pistol. There were three general production runs of this pistol - the early versions with the hooked trigger guard (all the rage in the 'Miami Vice' era) and S&W's own sight designs, mid-production runs with the rounded trigger guard and Novak 3-dot lo-mount sights and the last production runs in the TSW (Tactical Smith & Wesson) with some internal improvements and light rails on some models.
During any of these production runs you could also order the same pistol with an alloy frame (5903), in double action only in both all steel or with an alloy frame, with a decock only safety in lieu of the standard decocker/safety arrangement, with a light rail (later TSW versions) or without, with tritium night sights or without.
Oh, and let's not forget that S&W also made many models in plain old carbon steel in addition to stainless steel.
If you were a large law enforcement agency you could even have S&W create a special design for your needs. The FBI submitted a requirement for a 10mm pistol with a frame mounted decocker lever. S&W happily obliged. Later, the FBI ended up returning a few thousand of these pistols to S&W for warranty issues. S&W refurbished them and sold them to civilian distributors. Collectors are now going nuts trying to get their hands on one of these fairly rare FBI pistols.
So you see, there is no 'better' 3rd Generation model; there really is no turkey in the lineup. It is just a matter of what you can find and what fits your needs and shooting style. This is certain, however - if you end up like many of us, one is not enough!
