OK, Denzel is a biriliant actor and can cover both "good guy and "bad guy" parts (ranging from mighty Quinn to Training Day...).
However, Don Cheadle can really cover an incredibly wide swath, from Hotel Rawanda where he plays a soft spoken hotel manager turned hero to Out Of Sight where he plays one seriously scary bad dude! Miles would require that sort of breadth, IMHO.
Cheadle is one gifted actor. He deserved an Oscar for Hotel Rawanda.If you haven't seen that one yet, you should.
Just my humble opinion!
N