Would it be easier to change the upper control arm or just the ball joint on a 07 Yukon ?

Just have a beer and take to a cheap mechanic.

Normally when you need to change a ball joint, you need a press tool, or at least a really blunt hammer to pound the old one out. In a lot of cases, the ball joint is either integral to the control arm or installed in such a way that will render the control arm junk if removed. If the cost is not that much greater (which is usually the case), change out the entire control arm as it is less time consuming and if that option is available.

Watch a youtube video showing how to do it both ways and make a decision.

Replace the bad part on the vehicle that needs to be replaced.

As long as you have a good sized air impact gun, change just the ball joint ....................