Yes^^ I think the same thing. Neither would want to be the uke. It would be a battle each time (but in a canon way, it suits them as they're fighting with bodies or words each time one see the other). The winner of the fight would be the seme, without asking his partner of course, and as such, their lovemaking would be very violent and passionate. Lol.
But, actually, I can't picture neither Ichigo nor Grimmjow as a uke... so sad :'( ^__^
well with my yaoi glasses... i wanna say...
I SHIP GANJUxYUKIO!
ε=ε=(ノ≧∇≦)ノ