Bigger ain't always better. It's more about the ability of the dog than it's size. There is a point that big or little can hinder a dogs catching ability.
I don't like em too big and I don't like em too small.

I totally agree with The BoarNinja...I believe that the dog needs to be big enough that the hog has trouble slinging his head around or for the hog to get tired of slinging its head, this will reduce the chances of another dog getting cut down or worse yet getting crippled or killed. Just my opinion.
I have seen some smaller pits handle a big hog but these were wide, solid, quick, and no fat on them. I like a 60-65 pound dog.
I agree 100%, sometimes my 80 lb american is a little clumsy through the thick stuff but I've seen first hand him caught on one ear and another, smaller dog caught on the other and him able to plant his feet while the smaller dog is actually off the ground, we caught 6 toothy boas back to back pretty much this spring and I never had to put a staple in but huntin partner wasn't so lucky... we watched a big boar throw his 40ish lb pit around and into his teeth until we could get into the creek to him.