I've been having trouble finding out the strengths and weaknesses of various Mame derivatives. Heres what I have so far.
MAME The official build. It's command line based and obsessed with accurate emulation.
http://mamedev.org/MAMEUI A GUI version of MAME that is unofficially official (Or am I wrong about this?) comes in i386 and amd64 (32 and 64) builds
http://mameui.classicgaming.gamespy.com/MAME PLUS! An altered version of MAMEUI with enhanced language support and GUI along with automatic volume adjustment and other features (anyone care to add) 32bit only.
http://mameicons.free.fr/mame32p/MameUIFX Changes listed on the website includes bug fixes, auto volume adjustment, emulation tweaks autofire and highscore list support; 32bit only.
http://mame32fx.altervista.org/home.htmMameXT I'm honestly not sure what this adds besides support for a high score list. Comes in 64bit and 32bit.
http://www.mamext.net/