Federal HST in 147 grain. If it were a bigger short barreled gun like a Glock 26 I'd say there's no harm in the +P version, but with a skinny little PF-9 the slight (advertised as 50 foot per second difference between the two) gain in velocity is outweighed for most by the slower followups.
Expands very well, even at very low velocities, and 9mm doesn't really suffer much from being fired out of a 3" barrel. Heavier bullets lose less velocity than lightweights out of shorter barrels, and these days the velocity window for a bullet to expand properly is an independent variable, it's not some fixed number of feet per second that doesn't change even when the bullet does. I believe the heavy HST is supposed to expand well all the way down to 700 feet per second or so.
About 25 years ago when people first started using 147 JHP bullets, service pistol bullet design was in a kind of early puberty state, at the time the only bullets that would reliably expand were the lightly constructed bullets, light for caliber, driven as fast as possible. Revolvers used to have an advantage because they were insensitive to feeding, and manufacturers hadn't quite figured out how to make a bullet expand reliably and feed well in an auto without using the old lightly built/fast duet. They were basically making reverse-jacketed FMJ bullets with a hole in the nose.
Things are different now, there has been a lot of time and money thrown into researching how and why service pistol bullets do what they do, and while any bullet can fail to expand for no observable reason, or behave in ways no one could predict, we've gotten much better at predicting how they will behave the bulk of the time. Basically any of the current crop of bullets in 124, 147, or +P versions of either will serve very well as a defensive bullet.
