I always lean towards a white screen. Grey screens are nice, but once the lights are out, the bit of extra brightness is something I prefer. When the lights are on, you get a bit more punch as well.
I would go with the 130" Silver Ticket WAB or WVS. I would only use the Seymour Screen in a more critical viewing space with a better projector. Both screens are nice, and Seymour is of higher overall quality, but the Silver Ticket screens are still good quality. I have not used the WVS material, but it does appear to be a better white, which should make it more neutral, and perhaps a bit brighter for projection. It also appears like it may be better for 4K content. Once setup though, I'm not sure how much difference one could see between the two materials. I've used the WAB screen a couple of times this year with Epson projectors and they looked really good both times.