Based on what I own right now.
First choice (TIE): HK p2000 light LEM trigger. I have lots of spare parts for this gun and it is extremely reliable. Excellent accuracy.
First Choice (TIE): Sig P239. slim, easily concealed. Ultra accurate and reliable, access to 10 round mags if needed, no neutered mags.
I could easily live with either one of above as my ONLY pistol. Spare parts easily obtained from Brownells.
Second choice: especially if I didn't already have HK parts....Glock 19. accurate enough, reliable, the most size efficient 15 shot midsize 9mm, logistics of spare parts is excellent, if I lived in USA...access to 33 round mags if necessary.