There are a ton of good 9MM pistols available.
Does you friend have any experience shooting pistols?? If not or minimal experience you might want to recommend an entry handgun training class that many local ranges provide for minimal cost. They cover first safety and then basics such as stance, grip, trigger control, and sight acquisition including range time. It is very difficult for someone to pick out a pistol that will work for them unless they have basic fundamentals down. The old "it feels good in the hand" does not really cut it IMO. Training classes also often have a variety of pistols for the user to try out or at least handle.
Then there are preferences in size and weight, metal frame or poly frame, striker fired versus hammer fired, and safety or no safety. Also what the user intends to use the firearm for - home defense, concealed carry, range shooting, or a combination of these.
IMO for most people who may not have a specific use in mind a compact pistol is probably a good bet. By compact pistol I mean when where the users hand fits the grip comfortably and the length of the pistol is in around the 7.2 inch range plus or minus a little.
My PERSONAL favorites in 9MM based on personal experience in what works best for me are the Walther PPQ, SIG SP2022, HK P30L, HK VP9, SIG P226, SIG P228, Walther PPS, and CZ SP01 Shadow.
Out of my favorites the ones I recommend the most for that "first" 9MM pistol purchase are the Walther PPQ, HK VP9, and the SIG SP2022. These are all what I consider compacts under $600 range and the SP2022 in the under $500 range. The also have changeable backstraps/grips to help tailor the pistol to the shooter.
I also own a Glock 19 but for me I prefer the Walther PPQ and HK VP9 over it by quite a bit but if a Glock 19 works for your friend or anyone else it is a good reliable compact pistol.
Good luck.