For personal defense, the 640 with no hesitation

For collecting, the 2" 64

However, at $400 each, I would simply buy both

If you can not afford both in a single purchase, put a deposit on the pair with an agreement as to when final payment is due. In the olden days we called it Lay-A-Way

You do not have the instant gratification, but you would have two fine additions to your life long collection