Letterier's Hulk for me
The Tone, the other one is way too bright
The Detail, you can see the grain of the muscles, you can see the veins, just better
The Build, Old Hulk's face looks like someone with downs syndrome, his whole body seems to be modelled off of a really strong child (which worked well in Lee's movie and it makes sense to a degree), but New Hulk has much better proportions, and he just looks more like the comic hulk, I especially like the way they did new Hulks hair
The Expressions, okay Old Hulk has new Hulk beat for the Sad-Face, but that's about it, new Hulk is a way more expressive character
IMHO New Hulk, is leaps and bounds better than Old Hulk, mainly because of all the little details they did right in the characters design, I'm not saying the Old-One looks like Shrek or anything, but it's just not as good