I started out wearing fleece pants--basically sweat pants, but with straight legs instead of cuffs--with athletic long johns underneath. It kept me warm and a lot of the coaches dressed similarly. Then I read about skaters catching their blades on their pants and I decided to switch to leggings. I'm in Adult 2, still learning the basics, but I'm happy layering skating tights with thick leggings and a skating skirt. I don't bother with expensive name brand gear. One pair of leggings is from Old Navy, cost me less than $10 on clearance. The other pair is Vera Wang's "solid leggings" from Kohls.com, around $18, plus shipping. Now, the leggings are pretty narrow at the ankles, especially the VW leggings. There's no way to pull them on over my skates, so I just smooth them down past my ankles and put my skates on over them. Never had a problem with that.
I am too self-conscious to show my booty when I'm wearing skin-tight leggings, so I always wear a skirt, too. The main one I use is from Target, it's just a junior's mini circle skirt, very cute. I wanted another option, so I bought some knit jersey and sewed a short circle skirt with a yoga fold-over waistband. Very simple to make and a lot cheaper than most skating skirts.
I've never worn just tights and a skirt. I get cold enough as it is! If I removed the leggings from the equation, I'd be too busy shivering to skate. I don't know what I'll do when it comes time for me to participate in a competition, higher-level test, or show. But for now, I'm satisfied with my leggings/tights/skirt combo.