The PPQ seems to be high on almost everyone's list, but never having fired one, I can't put it there. I do, however, have a Walther PPS in 9MM and like some have mentioned, it is a great pistol. I shoot mine a lot and it is accurate, reliable, easy to take down and clean. I did add nite sites to mine because it is my primary carry gun and I walk my killer (lol) dog late at night.
If I were limited to just one handgun, it would be my Glock 22. It, like my PPS, works every time I pull the trigger and carries 15 rounds, my PPS only carries 7.
Again, I have not shot a PPQ, but Walther puts a lot of quality in their center fire pistols, so if you have ruled out a Glock, the PPQ might be the next best choice.