It's so cute how you take your cats for walks, and without leashes no less.
The gray one definitely seems smarter and more curious -- and appears to have a larger skull / brain.
Which is more talkative?
Bald their heads are about the same size. The difference in apparent head size is due to hair. As for brain size, keep in mind that brain size is not an absolute indication of smarts.
Neither is volubility, for often talky people haven't much in the way of smarts.
she has better verbal skills. but the black one is much better with visuo-spatial intelligence.