I spent months trying to decide what my new carry gun was going to be, I sold my Desert Eagle, and wanted something a little lighter, easier to carry, and in a more common caliber with higher capacity than either my revolver, or the D-E had to offer.
I look at Glocks, Baretta's, EAA, CZ, Etc Etc Ect.
The XDm felt best in my hand, and the controls were easier for me to operate being a lefty-shooter.
I would say figureyour price range first, and then shoot the models available in that price range to see what is most comfortable and accurate for the person making the purchase.
some people love the feel of one gun, but cannot stand others, find one that fits.