Only one!!?? Thats a tough one. Well it would have to be a nice one. If money was no object I would have to have a full custom Browning Hi-Power (Novak's, C&S,etc.). If I couldn't swing that, my second choice would be a Glock 19. Those are my 2 favorite 9mm's.
Just for fun, here's my picks for top 5 9mm pistols. Listed in order from my most favorite to my least favorite:
1. Browning Hi-Power
2. Glock 19
3. Beretta 92
4. CZ 75
5. SIG P226
Disclaimer: This is just my opinion. If you disagree with my top five please don't take offense because I don't mean any. Also, please don't take offense if your favorite 9mm pistol isn't even on my list.
P.S.: Isn't it pretty sad that I even have to put this disclaimer for fear of someone getting all upset about something so trivial?