I voted Howard. You could make a great argument for Lebron, but I personally just prefer the big man.
Put shooters around Howard, who can play D, and he can get to the Finals. Plus he can effect every possession on Defense, while still being a force on offense. Lebron can only guard his man.
Cleveland is a team made up of shooters, but until they get a guy who can be the "sidekick" to Lebron in the paint, they will have a hard time. Mo and Delonte arent a bad back court, their problem is their front court and their bench. Even Kobe needed Pau, you just have to have some form of a high level big man in the post.