Maybe use this,
https://vote.heliosvoting.org/Posted from Bitcointa.lk - #D5jZd9tVKCNLn5wCif others think that it's better if I select the 5 prizes straight away, sure
Yeah, less chance of cheating.
I disagree. I think voting would be best. Although voting can be altered, it gives the least amount of bias and would ultimately give better results than one person picking the top 5 IMO.