I've fired several 9mm handguns in the past 1.75 decades since I started shooting.
My personal favorite is the WALTHER P99:
It's REALLY ACCURATE. It fits my hand GREAT, and its adjustable to other hand sizes. It's REALLY ACCURATE. It has a good balance, whereas GLOCKS, and Springfield XDs feel front-heavy. It's REALLY ACCURATE. I like the sights that come stock with it. It's REALLY ACCURATE. I like the decocking buttons function. It's REALLY ACCURATE. It's very reliable. It's REALLY ACCURATE. I LOVE the light trigger pull (in both DA/SA). It's REALLY ACCURATE. The trigger is also capable of stiking twice if the primer didn't fire. It's REALLY ACCURATE. And with accurate fire placement, I doubt magazine capacity is of too much concern to me; Ten rounds is plenty, but more is preferrable. DID I forget to mention that it's REALLY ACCURATE? I'm not a good shooter by any means, but for some reason this is one of three handguns I've fired, and could get GREAT accuracy out of, YMMV. It's a great pistol all around (but I'd buy it in 40 S&W).
GLOCKS (17 & 19). I like them a lot, they're pretty accurate, reliable, have decent factory sights, high-cap mags... I'm just not a fan of their triggers, and lack of an active safety mechanism. Gaston was a F'in idiot for putting the safety on the trigger, IMHO.
Beretta 92. A decent gun, pretty accurate, less reliable than a Glock 17/19 in my experience, YMMV. I've fired over 300 rds in a Glock 17 without a hiccup. Whenever I fired my friend's Beretta 92 it jammed every 2-3 rounds with FMJ ammo. I field stripped it, cleaned it, and it then jammed every 6-8 rounds... Then I lubricated the SHIT out of it with gun oil, and ONLY THEN did it run perfectly fine. It DOES have an edge over the glock in my book because it, UNLIKE GLOCK, has an ACTIVE safety mechanism. A "Trigger Lever" type safety, IMHO, is NOT a safety. You'd be better off with the GLOCK or Walther, IMHO.
Really, all your friend should do is have you accompany him to a gunshop to find a gun that fits his hand well. Then make sure it has the desirable features (frame or slide mounted safety, sights, etc.)... If he likes it, buy it, inspect/clean it, try it, and see if he continues to like it. That's all that can be done about it, but you can help him through the process. Also, get him to enroll in a good firearm safety course as well! It makes me cringe to see yuppies buy their first gun (often a handgun), and NOT take ANY safety training courses whilst claiming "I think I can figure things out for myself..." [rolleyes]
Edited to add:
My post seems to have an ill-taste, forgive me for that...
But on my to-buy list, I have:
1911A1 .45 (Either Kimber, or other)
Walther P99 in 40S&W
RPB MPA-30 (Rail & Side Cocker Model) in 9mm with Sten Magazines.
and MAYBE a GLOCK 26/27 (but I don't really like glocks all that much; the price would have to be just right)