Greg at West, By God wants to upgrade his totin' iron. He wants something that will share a caliber with Beth's sidearm and that she will find easy to operate.
Well, if she's carrying a Glock, then nothing would be easier for her to use than an identical Glock. Plus they could share magazines.
No agonizing decision required: Get a 9mm Glock just like hers.
There, wasn't that easy? :)
On a tangentially-related note, I've never understood situations where the "His'n'Hers" home defense shotguns are a 12ga Mossenberger 500 and a 20ga 870 Youth Model. Either she should train to the 12 gauge, or, if that's physically impossible, he should realize that it won't hurt his manhood to use a 20ga Remington. Same thing with folks who are all prepared for the Zombocalypse with a manly .308 M1A for him and a dainty little AR for her. Either one or the other would be fine, but it's awfully impractical to use both.