So I've been playing the Darius Plus cart quite a bit lately. I used to be the biggest proponent of Super Darius CD, but lately I'm not so sure. The CD/arcade soundtrack used to be my biggest selling point.
The cartridge has really grabbed me: you can play it on your SuperGrafx with no flicker, and the PSG/PCM/whatever tunes are pure gold. Almost on par with the arcade, I can't believe this game isn't mentioned more often in best-of-chip-tune threads.
Right now, I give the cartridge the edge: beautiful chip music, and no flicker. What's your preference?