Always get the latest set, that is the one with the highest number. You don't need old sets as well. Some places may have for example the entire mame 0.108 set, plus a small upgrade to get from 0.108 to 0.108u1. In that case, get both sets. I'm not sure about a site that tracks these things, maybe have a look at maws or caeser. Mameox roms would be very similar to mame roms, but not exactly the same.