most use matt, but i've used gloss and i really like it, its up to you
this is gloss
a few tips for doing it, get a spray bottle with soapy water like you would with a window tint, and spray both the bumper and the back of the sticker, this is the only way of doing it without having to pull it off and back on to get it straight then cut two squares around the little lumps where the reg screw on, and start from the middle with a credit card, but use a hair dryer on the section your working all the time and it;ll go soooo much easier
not nessecarilly but if when your selling it on, say to a dealer, and they mention it, you can always so "o its alright that'll just peel off if you want", rather than "sorry thats painted on it would have to be painted over"
as a rule of thumb mods do make a car more difficult to sell