I just started playing the DoS version. I like the NES better. The extra dungeons are nice, but there isn't anything remotely like a challenge. The NES wasn't especially challenging as it was, but in DoS I consider a difficult battle anytime the enemy doesn't die in one hit.

People complain about null attacks in the NES, but they were a good thing. It made it so you actually had to think for three seconds instead of mashing the button all the way through the game.