Because of said "uniform," I've had quite a bit of experience with many a black jegging. Black jeggings are my comfortable, go-to pant that seem to dress things up a bit. I've tried the cheapies, I've tried the overpriced options and after a bunch...here are my top three black jeggings.
1) Citizens of Humanity Avadon Slick Skinny in Axel
These jeans look absolutely mini on the hanger but the four-way stretch is what makes them so fantastic and uber comfortable. The rise is a bit higher which helps mitigate against any plumber's crackage. Plus, they most certainly lengthen the leg line and thin out the thighs.
2) J Brand 901 Legging in Hewson
These classic skinnies host a thinner fabric, plenty of stretch and an ankle-ish length inseam. I wore the crap out of these last year and finally retired them after the fabric was worn a bit thin and the color faded. The pockets are clean and the rise is about average height.
3) Siwy Hannah in It's Magic
These super soft and stretchy little suckers are incredibly comfortable. The pockets are a bit more detailed, the rise a bit lower than average and the inseam is the shortest of the bunch - a true ankle length. While this pair wears and washes beautifully, they definitely stretch out quite a bit between wears. After three or four wears, these jeans tend to sag just a bit on me.
Beyond these three pairs, I've also heard from many a girlfriend that HUE makes an awesome black jegging. Has anyone else tried these?