I've got some post-lock Smiths and several pre-lock Smiths. I'm a shooter, not a collector, and each one of my guns serves a specific purpose. I've yet to see any fall off in quality between the older models and the newer ones. One of my favorite handguns is my 625JM, a gun that commits all of the sins that some on this forum continually rail about. It's stainless, it isn't pinned, the chambers aren't recessed, it has MIM internals, it was built on CNC machines and it has a lock. The gun shoots like a laser and has the tightest lockup of any revolver I own. There's absolutely no fore-aft play in the cylinder.
I do have one bias when I buy guns, however, and that is that I prefer to buy used over new. I love hunting out older specimens that are well broken in, perform well, and are priced reasonably. For that reason, and that reason alone, I'd probably go for the 27-2 over the newer and much more expensive model. The substantial difference in price between what one would pay for a good used model and the new gun does not justify any qualitative edge that the newer gun might arguably have (if there's any edge at all).
My 27 is a 27-3 4" that I bought from an auction site a couple of years ago. I paid about $550 for the gun. It's admittedly not a classic example of the gun, having been made in 1988 years after Smith stopped pinning the barrels and recessing the chambers. Still, it's a wonder to behold, beautifully finished, and with the capacity to put shot after shot in the same hole.
Btw, not to rain on anyone's parade but there's an urban legend floating around out there that the checkered topstraps on the pre-27s and 27s were laboriously cut by hand by some craftsman at Smith. Last year I read an article somewhere about the registered magnum and the 27, and, based on an interview with someone at Smith, the article reported that the checkering was always etched by a machine and never by hand.