i have both, use them every day (Unicomp at work and IBM at home) and enjoy them both. that said, there is a difference. the older the keyboard, the thicker (stiffer) the steel back plate. and the plastic has changed over the years from thick and brittle (model F), to medium thick and resilient (old IBM model M), to thinner. but if you are looking for native USB and a Win key, your best bet is a (newer) Unicomp.
the older boards often need some semi-skilled work to bring them into the 21st century. classic Ms might need a bolt mod and an active USB converter; terminals need a USB converter/remapper (like Soarer's converter - i prefer to put the adapter in the keyboard case) and maybe an ANSI conversion if ISO is not your thing.