Well, Undertale is more unique. At least the art direction is probably better for that reason. The gameplay is certainly more unique too, but I don't really like it better, or as much. Still, I'll probably go with Undertale overall. It's not like Xillia has the best gameplay in the world either.
Undertale's art is more unique but not at all my thing, and while Xillia's gameplay isn't even the best Tales gameplay, I'll still take that over Undertale as well
Undertale is very ugly but also absolutely oozes personality. It’s gameplay is also very unique. I’ll take uniqueness over any old anime action JRPG tbh