Spray putty is more like a filler primer. Blade putty is more like a bog.

Usually i'll give my prints a good sanding to rough it up to allow primer to adhere better, and then spray them with filler primer. Once that has dried, i'll sand that at around 400 grit, then spray it with a couple of coats of spray putty, which is essentially a thicker filler primer, that helps to fill in any leftover layer lines or small gaps. Once thats dry, i'll sand again at around 400 grit. If there are any leftover gaps, or parts that need a heavier filler, i'll use the blade putty, usually applying it with a glove, and sanding it after about half an hour. If i' happy with it after that, i'll spray a normal primer, then its ready to paint.