Walther PPS, either the classic or m2.
I went thru the same question when I first was choosing my single stack for carry, and I considered SIG p938 (which my wife chose for her carry pistol), the glock 43, and smith and Wesson Shield (primary alternative choice). I just didn't like the glock (too snappy even in 9mm when I shot it, and I just am not a glock fan), the Sig is awesome, but a little small for my hands, and I just really don't like the Shield's 2 point trigger. Chose PPS and love it. It's definitely fun to take to the range, and I was gifted the m2 by my dad and have grown to like and carry that one just as much.
I'd go with the Walther PPS 9mm 100%.