Thanks for the suggestions. The MR transfer benefit is not one I was aware of. That said, I'm less concerned about MR points; I have plenty of them and if they happen to accrue in different accounts, so be it.
My inclination is to go with the German card because I may move there for a while and can probably make better use of the targeted features (and benefits), which the ICC won't have. Managing it online (which I would have to do in the case of the UK card(s) when/if I move) is pretty easy. I suppose there are no other features which I've missed, so will probably go this route.