Reports are coming out from a few sources that using a conventional toilet seat cover is only good for your peace of mind when using the restroom.
It's being said that it doesn't actually have any effectiveness in regards to keeping you safe from disease.
Don't take my word for it though I'm not a physician.
However what I've been reading from physicians on different sites and forums suggests that the best way for you to not get sick when using the restroom is actually the one I personally catch people slacking on...
Good old thorough hand washing with water and soap!
So wash your hands under warm water with soap, and sing the lyrics to happy birthday, once the song is done that usually means you've washed long enough to make sure your hands are clean.