Bleh, task it to a designer direct, don't spec it out to a load of half-arsed incompetents.

There's a lot more to logo and brand design than just putting together a pretty picture. Most competent and capable designers would have nothing to do with such contests, unless there's some alternate reasoning (it's simply fun / it's for charity / etc)

Put it this way — how many decent brands do you know of that have come out of this selection format?

http://www.nospec.com/