Bear in mind that each person with a screen made up their own mind as to which screen to buy based upon their own criteria, and will often recommend the same product for reasons which may not be valid for you.
Differences - mostly differences in design, screen material, screen surface reflective properties (these may suit different projectors, viewing setups and ambient light levels). There are fixed frame, pull down, pull up, electic drop down, tab tensioned, rear projection and maybe more types.
Best screens - hmm the best is often very expensive, but Stewart have very good things said about them, as do Vutec, Beamax and others.
If you're asking an open ended question like this one, it's best to at least narrow down the enquiry by telling people what projector you have and what sort of environment you want to watch in.
I assume from searching for your other posts that you've got/are getting a Domino20, in a 7x7m room. That'll probably rule out any ned to use a grey screen that some recommend for LCD projectors, a white or moderately hi-gain screen should be more up your alley.