I wear PI ultrasensor shorts, and I've been really happy with them. I've tried shorts from both Castelli & Shebeest and wasn't happy with the chamois on either brand.
But - if you're looking for shorts for a 100-miler this weekend - if it were me I'd stick with the brand and chamois that I know works for me rather than trying out new shorts on a long ride. That may be a rather conservative approach, but I'd hate to be out on a ride of that length and realize part-way through the miles that I can't stand my shorts!
--- Denise