Do you use a stability ball when training your clients? If so what are your top five exercises?

Yes.
1. bridge combo w/Leg curl (hamstring) lying (roll-in)
2. prone plank (forearms)
3. toes on ball (straight leg bridge)
4. Knee tuck (progression to jack-knife) & knee side/side rotation (knees on ball)
5. Back or leg extension

Seniors:
1. Isometric hand over hand press downs & to sides for time (progression to cable or tubing if possible) seated
2. ITY’s seated
3. Adductor ball or fist squeeze seated
4. beginner (on knee) prone back extension/scap squeeze
5. Wall squat