I use the fullmask paintball kit. Fogtech halts essentially all my fogging issues, if I happen to have any. I also happen to find it comfortable and proper fitting, and I have no issues sighting through my RDS. (I use a FA-MAS G2 Sniper, so I have retardedly high sights + rail+ RDS itself.)
It's a matter of finding the balance between what you consider acceptable risk and ease of gameplay. With proper use, you shouldn't have any problems with a full mask. Plus, you can always modify the mask so it doesn't interfere with aiming down your sights. (Greylocks can probably inform you as to how it is best done.)
Personally, I'd prefer to not have any marks on my face, seeing as how I'm incredibly vain and I also have to look presentable for work if I want decent tips...bleeder wounds just don't say, "Your vodka + cranberry is worth 40% of the price in tip."