Whoah i don't even know 50% of those on the list. Would have been a little more cool if you could choose a country instead of alot of small units that allmost nobody knew existed.
But my choice goes for the Brandenburgers, they were savage and sucessfull in what they did. If you can sneak into a heavy defended city disguised as NKVD's inspect all the defenses and even execute some conscript deserters you gotta be a sick bastard.