I think placement is placement of events. If so I'm surprised so many people consider me to be good at that. The only placement I put any thought into is where enemies go (I try to be as devious as possible, especially on hard mode). But when it comes to ammo/gems/etc it's mostly an afterthought for me, and never put much attention into it.

In any case, I think p4ul's levels have the best EC, hands down. I can always tell it's one of his levels just because of the stunning use of tilesets.

For gameplay, I'm going to say blur, because he has made a huge number of very unique levels. Far more than anyone else. For regular ctf (or other gamemodes) I also like firesword and stripe's levels.

I can't think of anyone for the other categories.