I'm gonna go with Lobster Zero, not because it is really my fave, but I think the Manta-gon looks kinda like figures that have been done allready. I still like the Ika best. Seems very original.
Frank, which one would you rather be if the two of them were tossed into the fighting ring? For me, it's a clear choice: Lobster Zero!
Both designs are cool (great art, Creepy!!), but I vote for Lobster Zero. Funny, the vague "He-man-ness" is something I like about it... (bigtime MOTU fan growing up, what can I say?)