I've carried four 9s and liked them all.
Of these, my favorites are the Springer and the Steyr S- it's a tossup. My vote goes to the Springer due to the availability of holsters and accessories.
The Springer and Steyr are both tight, well built, accurate guns and VERY ergonomic.
Although some will tell you the 9mm isn't enough for SD, I disagree. Ballistics tests show it to be almost equal to the .40 S&W, and people have been being killed with it for decades.