Depends what you want to do. IDPA, IPSC, Home defence, Target shooting, etc. My first 9mm was a Glock 17, and it was a great choice as the G17 is such a common pistol - many inexpensive accessories such as sights, barrels, holsters, etc are available. Also digests all types of ammo. I've put approx 5000 rounds thu mine of various ammo and have not had one problem (caused by the ammo - I've screwed up with magazine insertions, etc.) And to top it off it is an inexpensive gun.
That being said, I have a sig P226 (in .40) and a CZ 75b. I shoot the glock competitively so it is my 'go to' gun but I have to say my CZ 75b is an amazing firearm. The Sig is great as well - All are different and have their strengths.
So - Figure out your shooting goals and budget and enjoy!