Better use of the color green, grunge style is much more effective, and overall composition is better.
It just looks better.
Though the tones of the signature could have been better (the whole thing basically looks white and one shade of orange), I like the composition better. It`s more eye appealing, though the contrast in Vai`s sig almost won me over.
Both signatures were done really well, but Haiko just seems more visually appealing. I think it`s the use of color and deep contrast.
Though Jono`s sig is huge, nothing in the rules stated size restrictions, so it being big should have nothing to do with the voting. I choose Jono`s because of the extremely clever idea and it`s just visually appealing overall. The way MMOG was demonstrated is very clear and the web 2.0 style is also clearer.