Lots of options.
Can't even remember exactly which one I voted for without looking
Anyway, I'd say once this has been tallied up we should maybe take the top 5 and vote on them, by mappers who might map for the contest.
The reason being is that while alot of people might want new gamemodes it's possible that alot of those votes aren't even from people who would seriously try the contest out.
Custom gamemodes aren't easy to think up, easy to implement... I know a few people around here could rig something up, but that's almost like having a modelling contest.
It's probably best keeping to TF2 standards to a degree so that EVERYONE can make a map. Dealing with entities for cap points and whatnot can be a struggle for some, hell, I just copy paste that stuff as much as I can.
On top of the difficulties of making it then you have to test, everyones gotta learn x amount of gamemodes. If you don't know how to play it's not as fun. So if a map doesn't get enough gameplay for you to even learn the new mode...
Then you gotta judge them. Base it soley on how much fun you think it is? If so we should use one base map so all gamemodes get tested on even ground.
Because you can't judge gamemode on how the level looks.
To have a successful contest it probably needs to be something all mappers AND players already understand and have it based more on the overall map design and playability rather than a subjective 'how much fun is it' type of vote.