Xelement5x in 3... 2... 1...
See, if people post on the weekend I don't get to them until Monday when I'm back at work normally
Thankfully, this saved me a lot of time since SamIAm basically said pretty much the same thing I did.
I cannot totally comment on the PCE one as I have not finished it but I did play for quite awhile. Visually it's quite stunning, but the Sega/Mega CD version is still my favorite. Like Sam said, the localization of it on the SegaCD is wonderful (to me at least) and all the tongue-in-cheek references make the game just so much more than another generic ARPG.
However, like he said the difficulty bump in the US version makes it so much more grindy to play through, but that is Working Designs for you. There are beta copies that were sent to press where the difficulty from the MegaCD is retained so it makes me think the difficulty increase was a later decision in the process, possibly to help lengthen the game.
In general the PCE one seems to play quite well, but the humor and dialog in the SegaCD version still make me love it the most.
Oh, and like other said yeah don't waste your money on the SFC version.