heh UAC and Strongman are two of the 5 I'm missing (but I have Veteran from challenge modes). Reaper is probably the easiest to specifically aim for, but that would be a bit boring IMO - you can grab that one along with others in any successful game with a homing phase or even with regular phases. I'd go for Berserker (aim for the Gold and the Longinus Gold, you can get Reaper and Scavenger as well if things go well) - or any other Angel really. The advantage with Berserker is that even if you fail, you might get the silver.