The zebra definitely, the colors are beautiful and very bright. In fact, I think it would look good on a t-shirt.
Just like everyone else here, I agree with the Zebra. Not only is it something that is rarely done, but the colors chosen are perfect for it. Truly amazing. Great job on the rest. Second to last one really hurts my eyes though... Not because it looks bad, but because of the slight illusion.
The first one. 2nd does not catch my eye. 3rd one...I agree with Frag Man, it is overdone. The zebra came close, but I just like the 1st one better.