Hey Chris. I'm new here myself, but I've heard many troopers go the plastidip route. In theory it gives a nice, professional look with a smooth texture. However, as I am learning the hard way, it can be a pain to get that stuff in there and coat the proper surfaces just right. IMO a flat or satin black spray paint would work just as good but give you less hassle as it will: 1) Dry quicker, 2) have less likelihood of spilling out through the crevices in the helmet, and 3) just be easier to apply in general.
Regular paint, when applied in thin coats will adhere to your plastic just fine, without being too runny, but as I've found with plastidip, it goes on like a thick sludge, and you gotta kinda roll the bucket around so the stuff can cover everything.
One last note on plain paint, you may or may not need to apply a base primer to give your finishing paint traction.
Like I said, I'm a rookie; just throwin' in my two cents!