Before asking "What ammo should I use?" you should ask "What should ammo do, what shouldn't it do, and how is it tested?" I recommend the following:
Handgun Wounding Factors and Effectiveness from the Firearms Training Unit of the FBI
Basic Wound Ballistic Terminal Performance Facts by Dr. Roberts (DocGKR)
Ordnance gelatin test assessment for rifle and pistol calibers by Dr. Roberts (DocGKR)
What's Wrong With The Wound Ballistics Literature And Why by Dr. Fackler

For specific recommendations I start here:
Service Caliber Handgun Duty and Self-Defense Ammo by Dr. Roberts (DocGKR)
Then here:
9mm Ammo Quest on Youtube by ShootingTheBull410

I chose Federal HST in 147 grain standard pressure (P9HST2), but it can be difficult to find.