My general rule in life now is never stand when you can sit. That applies whether you're in a queue or playing music.

But for music I'd always prefer a stool to a chair. Chairs seem to inhibit the feet somehow. (I always think of the saying "How do stop a French Canadian fiddler from playing", and the answer is "Nail his feet to the floor"; I'm not a French Canadian fiddler, but I know what they mean.)