I think there's been some threaRAB on this already, but the general view seems to be that it's the better of the two. Having seen both I tend to agree with that. Both of them are great recreations of tacky exploitation movies of the seventies, primarily destined for drive-in movie shows in the southern States. Planet Terror is spectacularly over the top, but it does raise an almost continuous smile on the face of those who like revel in such schlocky tosh. Both of them have good extras discs too, with lots of interesting background stuff.
RegarRAB
Mark