Definitely the Piano version. Although I thought the rock version was cool and inginuitive, the piano version suits the show a lot more. I can't wait until Key drops their emotional bombs on us. This series is so amazing.
both versions have been taken down now, but dang that is just awesome that they kept the beats and lyrics 100% on with each other. I'm surprised they didn't put a little solo or extra riff or something.
Remix sounded great, but I still liked the piano best.
I like them all. Although the remix could be better if one of the versions was replaced with an instrumental. When one is available of course. That would cut down on the echo/reverb of the singer's voice, which is IMO the only negative aspect of the remix.