What is the best car, truck, motorcycle, watch, loud speaker, headphones, camera, power drill, dish washer, wine, beer, pillow??
Here are some candidates for 9MM pistols IMO from currently available mass produced non custom models.
What will be best for a particular shooter depends on budget, intended use such as all around/CCW only/ range/ competition/ home defense/professional, how the pistol fits a users hands/fingers, preferred trigger action, and ultimately how well he can shoot it.
Metal frame hammer fired:
SIG P225/226/229/239
CZ 75 series
Beretta 92 series
Browning Hi Power
Sphinx SDP (mostly metal frame but poly grip)
1911 9MM - Dan Wesson, etc
Poly frame hammer fired:
Anything HK including USP/P30/P2000
SIG SP2022
CZ P07/P09
Beretta PX4 series
Poly frame striker fired:
SIG P320 series
Glock 17/19/26/43
HK VP9
Walther PPQ/P99/PPS