I've used MAME almost from the beginning of the project and love it. But today there exist so many variations and "distributions" of the original that I can't keep count. I used the MAME Plus project but today I like the MAME Plus! XT a little more. I'm looking for a version that uses a multicore processor better, but any suggestions would be appreciated. I also prefer the ones that keep up-to-date with the original project. Thanks in advance.
There are 2 main versions which together will play pretty much everything. For the official MAME, get MameUI64: this version has a nice user interface and is 64bit. Winkawaks is used for some Capcom games which run on a different chipset to MAME.
Everything else seems to built on top of these two.