Just like in any film that is in preproduction, pages of concept art is created before a final version is chosen.  An interview with XSIBase.com designer Aaron Sims reveales that he was part of the process early on before a script was even written.  As to the final product of designing the Hulk Sims says, "The inspiration really came from the comics, searching through character's history and working with the director to find  that Hulk everyone wanted to see."  The Hulk really did look crazy cool in the film but now you can see early concept art for the Hulk and Abomination both of which are awesome.  Click the photo below for the full interview and more photos.

Source: io9

-Phil