I carry a S&W 327 TRR8. It's an 8 shot .357 mag revolver. I'm a revolver kind of guy, and am not as fond of pistols.
As far as what works for your father, go out and let him shoot as many different handguns as you can. You need to find the right one for him. Different manufacturers have different physical designs that fit in the hands of people differently. You need to find a gun that fits your Father, and a round that he can comfortably shoot.
No two people are the same, and no two guns are the same. Similar potentially, but not the same.