Okay, so, Knights.

I can't resist the lure of these war-machines, but since I'll probably only get one, I want to make sure I get the most bang for the buck. And while it used to be easy -- have the Knights codex, you know all the Knights -- there appear to be a ton of FW Knights and possibly even other dataslates/rules/etc. found elsewhere.

So: where do I find all the Knights available? And what suggestions/advice does anyone have about choosing the right one?