Now, with that being said, you did put this up for vote and are looking for input.  It depends on what you want here, if you're trying to add more drama and controversy, then I'd say absolutely go for negative votes.  This will pretty much polarize everyone even more and probably give two bands a huge amount of votes, one from each side.  Do you want the Neoprog and the Zeuhl camp to loose their favorite second place band?

Also, if you do a negative vote poll, then you run a much better chance of people voting out of ignorance.  Let's say there is a poll of nine bands, of which I'm familiar with five of them.  There's a good chance that I like the five that I know on some level which means that I'd vote to eliminate a band that I'm utterly unfamiliar with.  Admittedly, this doesn't sound overly fair to a band like "Grails" who I simply haven't heard.  On the other hand, if I'm voting a positive vote, then I'm at least voting from knowledge and experience rather than blind luck.

As I mentioned, this is really your tournament and with the work that you're putting into it, you get to decide what you want to do and frankly, we really don't have much of a right to complain either way.  Nonetheless, I voted for positive votes.