Yes, I have their skinny jeans. They are an amazing color of denim - a deep blue. I would love to have bootcuts in this wash.
They are lower rise than the COH, but somehow, they work on me - and I usually hate low rise jeans. I have problems with lower rises falling right off my hips - but there's something about how they angle from waistband to hip that works. For reference, my hips are 33 inches and my waist is 28 inches; there's only a few inches between belly button and hip bone, and hip bone and widest part of my hip; I am also the buttless wonder. These really look good from the back view - they hug in the right places, which is saying a lot, because for example my COH are looser in the butt (still look cute, they're just looser).
They aren't as stretchy as COH and the denim is thicker. That's a good thing for skinnies worn in winter with boots.
As for white jeans, I don't know if I'd pursue this brand. They are my most form-fitting jeans I own, and I'd be worried that they would be TOO tight for a white jean. For white jeans, I have COH Amber's.... after a long exhaustive search, these were the best.
I don't like the fit of JBrand, so I'm not going to be much help there. There's something too.. long... about them in the hips; they bag around the butt for me, and their pockets are too large making my butt look fat and it's sooo NOT fat. I also just don't like the way they feel on my skin, and many of their styles have orange stitching which I hate. I like the stitching to match the jean. Somehow I find this is more slimming on me. Or maybe I'm just too short for contrast stitching and it overwhelms me?