Cover B is actually the hotter of the two. According to discussion in the Black Science thread the print run was originally supposed to be split evenly between the A and B covers, as it was for issue #1 (ignoring the variants), but apparently that went out the window and most retailers ended up getting shortchanged on cover B. So it has become an incentive variant of sorts. Of course nobody knows the number breakdown between the two covers, but cover B is definitely the lower printed of the two.
Both are worth grabbing for cover though, as this book likely saw a significant drop in print number from issue 1 to issue 2 but reviews have brought demand back to it. The 2nd print for the first issue releases next week with the 2nd print for issue 2 releasing towards the end of January, I believe.
+1
I have been picking up extra copies of 2 B at Midtown Comics, as most of the people selling #2 on Ebay are selling the A cover. I have noticed a lot of these books were damaged, took me a while to pick out 5 nice copies.