I don't have comprehensive knowledge, of course. I can only report on what I've tried, and that's limited by what's available in the LBSs where I shop.

I've liked tights by Sugoi and Endura. My favorite insulated tights are Endura's Thermolite Biblongs. There' durable as hell. I got two years of daily riding out of my first pair. If you ride only occasionally, they should last for years. I also came across some Trek kneewarmers I really like. They actually come in sizes instead of one-size-fits-nobody. Shopping this season, I find Endura makes kneewarmers in sizes too.

It's interesting to see the different ways by which they accomplish the articulated knee. I haven't seen much difference between those that sew a larger panel in the front over those who sew a smaller panel in the rear. Either way there's a little bulge in the front for the kneecap to fit. It's nice when wearing one layer and makes a world of difference when wearing two.

I still remember my second winter, when I was using cycling-specific stuff for the first time and didn't yet know the things I shared above. I had regular tights--not wind-front, so I had to wear a baselayer beneath them, plus kneewarmers when it got cold. I could barely pedal. My third winter was when I learned about wind-front stuff, insulated tights and articulated knees. Boy, what a difference that's made since.