I own a 5-inch Charles Daly (not very good, my first pistol), a 4-inch Stainless Kimber Pro Carry II and a 3-inch Kimber Ultra Carry II. Both Kimbers have worked flawlessly for me, and the 4-inch is my go-to pistol. I put Meprolight tritium sights on both and I've been pretty pleased. I'm jonesing for a 5-inch stainless Kimber to match the 4-inch.
As for shot placement, zombie lore is usually no more specific than "destroy the brain." However, I would think that destroying the frontal lobe would be best because it's big and controls motor skills. Severing the brain stem from the spinal column should also be pretty effective.