I'd pick black out of the 2 myself but it really doesn't matter what any of us think would look better. I always thought it would be cool to split some covers and make zebra p90's. I would have done it a long time ago myself if I was into P90's and had a guitar with them.
Offhand I'd say black - but that's without seeing the guitar.
Pickguard or no? With pickguard, black might be too much.
Chrome could be cool too, again depending on the guitar.
Personally, I love the look of these bar-pole P90s from Jerry Sentell - cutout cover and clear bobbin.