Personally, I go for the X68000, simply because more effort goes into coding music using PSGs or FM chips, as opposed to simply telling it to play a specific CD audio track, which the FM Towns does. And it sounds better than the arcade version, as opposed to most x68000 ports which often have practically identical music to the arcade versions.
Sometime I find games with CD audio tracks have music that doesn't compare well to the arcade original. For example, I much prefer the music of the arcade version of Death Brade as opposed to the FM Towns version (although in MAME 0.139 someone seems to have increased the ADPCM volume waaaay too much).
http://mahlemiut.marpirc.net/fmt_deathbrade.avi (for comparison, as emulated by MESS

)
I guess I could make a video of the x68000 version also, if you can stand the annoying disk swapping.

We'll ignore the SNES version, since it just plains sucks
