You can pick four musical artists...

... who are going to be locked away in a studio for six months. During that time they will write songs, rehearse them, and then when the six months are up they will perform them on stage to a large audience.

What four people would you put together to create the best show? You can pick any four people (dead or alive) and you will get them in their prime. Obviously they need to be not only talented artists but have talents that mesh well together. Somewhere in there you need songwriting talent, vocal talent, instrumental talent, showmanship, etc.