I have a pair of black and white ocellarius (Orca and Shamu) in my 45 gallon and 2 small Rod's onyx clowns (no names yet) in a 10 gallon system. Can't go wrong with either one. I love my pair of black and whites, they are completely jet black, I puchased the feamle through swf.com and got the male at Ocean Design (very good LFS).
You can't lose with either, they both are great looking fish. But if you want to puchase black and white ocellarius I recomment Ocean Design. They are tank raised and they are quarantined for a week or so. OD always seem to have healthy livestock.
P.S. buy 2 if you can,