RFESS (Rear foot elevated split squat) is pretty good for tennis players. Not saying squatting is bad - or deadlifting is bad.
Why I like it is its basically 'instant' with regards to learning. If you do your first set starting in the bottom position - you can get the movement right away.
Whereas learning to load maximally on squats and deadlifts can be a time consuming proposition. The thing is really the best way to get good at tennis is to play tennis. If you end up spending a lot of time learning to squat heavy while staying healthy your tennis is going to suffer.
I am not sure its world's greatest lower body exercise - but it could be. Its easy to load - and its unilateral.
For upper body throwers ten is nice - because it adds some zip to your serves.
I dunno about you but as rec tennis player - I want to play tennis. Thus we need to always be seeking exercises that maximize bang for the buck.