The differences between various types of Old West style holsters is largely cosmetic, and up to the individual. However, so far as "one size fits all" or at least many, is concerned, that can be another story. In general, holsters for Colt's Single Actions will probably be a bit small for, say, Ruger Blackhawks and Old Model Ruger Vaqueros. Open-top sixguns may also be a bit loose in holsters that will take a Colt's SAA. Obviously, a holster for a Colt's SAA will be way undersized for, say, a Walker Colt's or a Dragoon.
Style-wise, the slim jim holster (sometimes called the "California-style") dates from the advent of the "belt" revolver (1836 or so), as opposed to the saddle holster which were generally used to carry heavy Walker Colt's and Dragoon revolvers. This style carried over into the 1870's when the "loop" style began to appear in the Southwest, apparently coming up from south of the border, and spreading north even beyond the Canadian border. Shoulder holsters came in sometime in the 1880's, mainly for gamblers or businessmen, etc. The drop-loop style, with an extended belt loop formed by the skirt of the loop, which passed over the top of the belt was seen from the 1880's, especially on military holsters worn with the wide canvas "prairie belts", and were sometimes seen into the early 20th Century. The Buscadero rig, where the holster's skirt passes through a slot in the belt, and sometimes with the slot in a lower extension of the belt body, is pretty much a Hollywood invention, commonly seen in older Westerns.
As was stated above, the book Packing Iron gives a lot of detail on the various types of rigs. What you choose will be up to what sort of character you want to portray.