I think we're getting rather far from the original poster's question. He is comparing to a 70 tommer, so he's looking for something small.
Small steam covers 0-6-0s; 2-6-0's; 4-4-0's 4-4-2's; 4-6-0's, and maybe some 2-8-0's and 0-8-0's.
Medium steam covers 4-6-2's 4-6-4's and 2-8-2's.
Large steam covers 4-8-2's 4-8-4's 2-10-2's, and on up through the articulateds. There may be some overlapping of wheel arrangements. For example there were some pretty big 2-8-0's and one or two downright huge 2-8-2's (the GN 0-8 comes to mind) Some of the 4-6-4's got pretty big too. Look at the larger Santa Fe 4-6-4's

Anyway, I think he's looking for a nice steam switcher, and not very likely a brass one.
Brass is a world unto itself, and I will have to disagree about the level of detail versus plastic. Oh you might win that arguement if you were comparing 1960-70's vintage brass to current state of the art plastic, but current offerings are much more detailed than their plastic counterparts, as they should be. Many are equipped to receive an operating front coupler. They just aren't shipped with one, as many brass buyers display and don't operate, but it's a pretty simple matter to swap one out for a functioning coupler if you want to.