My first S&W was a M29-2 6-1/2". It did have some holster wear, and although I did buy it from a gunshop, I met the previous owner. He shot it regularly with magnum loads, but it still locks up tight. It brought back a lot of memories for my father, as he bought one the same year I was born, so I gave it to him (I still shoot it though).
I then picked up a 629-1 4" in trade. I've only put a few hundred rounds through it, but I absolutely fell in love with it. I do find that, with the 4" barrel, it's more pleasant to shoot with a 240gr cast bullet over 10gr Unique. It's a nice mid load. Heavier than a .44spl, but not the hammering of a mag.
I also had a 29-3 4", but I traded it to a friend. I carry my handguns a lot and the finish would have just been worn off of it, and it was an absolute beauty. The trigger was not as nice on that one, though.
If it were me, I'd stick with the 629, due to the fact that it's easier to maintain, especially in the very humid summers around here, and it does not as easily show holster wear.
But, if I could only have one, it would have to be that 29-2 6-1/2". It's just a beautiful gun with a perfect barrel length.