In a straight up fight barring the Force the MC takes it. I think the Chief is faster and Obi-wan's flesh is still verily much human. His shield may allow him to survive a lightsaber hit or three, as shields do seem to be quite effective against lightsabers [i.e Droidekas, personal shields]. However the Force [i suppose it depends on how creative we think Obi-wan is with it and whos interpretation of force power levels we are taking as red] should mean he can feel the MC through the force, level amazingly high pressures on him; crushing him, rip him apart, throw him miles into the sky and watching him die from the crash landing etc etc. Given a situation were the MC has to hunt Obi Wan down...Obi is one deaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaad Jedi.