As you probably know the II has shutter speeds from 1/500s through 1/20s. The III added some slow speeds down to 1 second using a dial on the front of the camera. The IIIa added 1/1000s to the upper end. All three of these cameras, and the IIIb I believe, are the same size. All the pre-war versions are nice. The IIIc came out with a stiffer body and it is probably the one I see recommended most often. It is nice, but unless you start using the faster and larger 90mm and 135mm lenses I think that the earlier versions are plenty strong enough. Just my opinion of course, there are some who feel all LTMs are best left to the collectors and the M series better for users.