That's a really hard choice, there are some good games there, but of those I think I'd go with Lunar, especially since it's the SCD version, because it's pretty short, well written, and funny game.
I'd also highly recommend Phantasy Star. I wouldn't call the graphics terribly dated other than the fact that they're 2D, which is a big plus in my opinion. Yes the village sprites don't move, but it has first person dungeons, and animated monsters (which is something you can't really say about FF until the PSX). What PS is though, is hard and, at times, very frusturating.
I'd also recommend Xenogears, but it's very talky, and if you're not willing to sit down and really get into its story, it's probably going to bore you. It has some serious flaws though like the fact that there is very little chance to go anywhere other than where the game tells you to, the second disk seems very rushed, and most of the characters don't seem to be very fleshed out, which is a pretty big problem considering the only thing Xenogears really has is a terrific story. One thing about Xenogears though is that every time I've played it, I've never had to do any serious extra leveling (the characters seemed to naturally gain enough levels just by fighting the monsters on the way to the next area) unless I wanted to.