North American PSII box art, no contest, but only because it looks nothing like anything going on in the actual game. Although, the front of the Japanese version of PSIII's box art is pretty horrendous, too. It was said best here:
http://lparchive.org/Phantasy-Star-3/You know, if Rolf and Nei really did look like the box art, it would have been cool and very in keeping with many of the middle-aged sci-fantasy heroes of the 1980s, but we all know that in no point in the history of gaming has any JRPG ever had heroes older than 20 (Amy is 23 and Rudo is 35, but they fit other common companion tropes). Ah well. Would have made for a really cool grizzled war veteran story, but alas, 'twas not meant to be.