I definitely prefer to grill chicken breast, not smoke it.
Marinate in citrus, lemon or lime, oil, garlic, maybe some adobo (I love the stuff), black pepper, fresh herbs such oregano. Italian salad dressing works if you wanna go quick and easy. Lemon + Oil + whatever you want, just keep it pretty simple.
Get the fire hot but not TOO hot, depending on how thick the breasts are. I don't like them too thick.
Like ButtBurner said, take em off as they start firming up and a taaad bit more. The last thing you wanna do is overcook. Get a good char and let em rest under some foil.
Healthy, versatile, quick, and so tasty.