I'd start by deciding on a budget and screensize. After that a quick way to throw out about half of the options is to decide which color fabric you want. White or grey. Your choice will depend on your choice of projector and the viewing conditions.
White is the default choice but grey can work to fix certain problems. For instance, if you're going to be watching with lots of ambient light grey can help black levels. You will need a projector with plenty of lumens to compensate for the dark screen though.
Something else to consider, where will you be putting your center speaker? Keep in mind that there are "acoustically transparant" screens that allow for a speaker behind the screen.
I went with screenpaint btw (grey), works a treat!