Hokay...

Fire: Fourth one. The second one looks like Black Spy from the old Spy vs Spy comics. :-)
Water: I think the problem with them is they mainly look like they'd be better suited for electricity, not water. However, given the choice, the fourth one.
Metal: Second one.
Earth: That "Do I have a choice" one looks good. :-) Nah, the rightmost one.
Air: I kinda like the second one, really.