the cooler master or k90. i would say cooler master just because all the switches are mechanical and some of the k90s are rubber dome, and i just don't care for corsairs mechanical boards, but that's more a personal issue than a fault of they keyboards.
the k90 gets dirty really quick i've heard because of the open design, and the delete key isn't cherry mx which would bother me and the blackwidow isn't cherry mx red
so, neither get the rosewill cherry mx red keyboard
if i had to pick, I'd get the blackwidow simply because it's not open design. Even though cherry mx blues would slow me down. I use all the keys on my keyboard quite often, so going from mechanical to rubber constantly would be anoyying which would make the k90 a poop choice for me.