Even with all the great commentary so far, I would like to weigh in.
I think Reid would most likely win because polling shows Republicans are less likely to vote for a Mormon for president. Logic tells you that as well. Naturally, they are going to vote for Reid, so there would be a great amount of apathy on the Rep side, both in voting and activism. This results in a Reid victory, handily in electoral votes, but just slightly in popular vote. Maybe a 300-238 (just an estimation) and a 52-48. Narrow victories and even lower than normal voter turnout would be the headlines of the night.