If you are going to be doing any repetitive assembly and dissambly you need to get a set of steel punches, make does not necessarily matter. I have had cheap ones and high dollar ones and they all eventually bend, break and mushroom out. Craftsman tools have lifetime replacement, which is what I have been using for a while now, so I don't worry when a small punch goes "tink".
Roll pin punches are worth their weight in gold for roll pins, and I highly recommend getting a set if you are going to be working on AR type rifles. They center the punch on the pin. I usually start a pin with a standard punch and then finish up with the roll pin punch.
Brass punches are nearly useless. They mushroom out badly, they WILL marr a finish, and they WILL dent steel, despite what you would think, or what some know-it-all has told you. They are best used when hard beating is required to get a part OUT, where steel punches would terribly distort the steel. Removing handgun sights, such as on a 1911, comes to mind, but I start with a wood punch made from a dowel, first.
Marring can be minimized by adding a drop of lubricant to the surface being "punched". This reduces the friction between the two surfaces, however slip-off is more likely, so you may want to pinch the pin and punch with your fingertips, thus holding them together.
I have a lot of professional experience working on guns, just not AR rifles.