Leggings are my favourite piece of clothing during the week, just because I can combine them with everything and feel comfortable at the same time. I picked those two outfits where in the first one I combined a very common black pair of leggings and in the second an edgy pair.
I use to wear this kind of black leggings from Garage also when I am running or at the gym. I also have similar ones in dark and light grey, they also match with all the colors.
The second pair doesn't match with everything - I normally wear it with black or white - but I like the leggings with patterns as well (flowers maybe?). They look lovely in summer with white tank tops.