Purchase a centerfire defensive handgun you BOTH like, for the second gun buy a 22lr in the same type, revolver or auto.
It's one thing to purchase, it's totally another to feed it. To be profiecient with a handgun means trigger-time. You'll get more out of the 22 because the ammo is relatively cheaper, recoil is negligble, and you concentrate more on proper sight alignment, grip, stance, etc.
Another consideration is to get one that is ultra-concealable, plus a second one with max stopping power. Any handgun that you have on you beats one left home in the safe. There will be times when concealment is the major issue, there will be other times (like when you have to drive through a lousy area of town after midnight) when concealability is less important than stopping power.