Here in southeastern Oklahoma, we have the same situation as Hunter does. The greys are a lot smaller than the reds (also known here as Fox squirrels)
The greys hardly ever sit still and are always moving, making them harder to shoot, and not enough meat for me, so I go for the bigger Reds. They seem to sit a lot longer, and use the tree branches to hide from you rather than running so much.
I have a pipe feeder in the front yard of my cabin, at the lake, because Mrs.WBB likes to watch them in the morning. Every day I will see at least 25 to 30 greys come to the feeder. I only have one Fox squirrel that comes to it, but he is always the first one there, and perchs on the feeder hole. The greys don't seem to have enough brain power to know they can run him off because they out number him, and he seems to be smart enough to know, that if he pushes a little corn down on the ground every so often, that it keeps the greys busy on the ground, and he can eat until he gets his fill, without being disturbed.
That may be why they do so well in certain ares, is because they may just be that much smarter.
Just another 2 cents spent.