#1 looks cool, too bad this is a design tournament.
#2 looks too generic apart from the 4wd, plus the splash is boring.
#3 looks decent.
#4 AHHHHH! MY EYES!!! That doesn't matter too much though, because the bot itself looks rather good.
#5 looks effective. Makes you wonder about the setup. Decent splash.
I vote for #5 ^_^