@scathach 45 colt is ok to shoot, but i find their mostly in revolvers and i dont find many revolvers to be very ergonomic. So they tend to hurt your hand ifyou shoot it too much, not to mention being a pain to clean.
A 10mm has 50% more energy but, at least in my gun, is much smoother to shoot. I'd say for handguns 10mm and 9mm will cover you well enough... if you really want a variety a 45 ACP is nice, as is the 5.7mm