Bane

I’ve been devouring a bunch of Batman comics lately, most recently Batman Eternal. The sheer amount of villains I’ve read has got me thinking a lot about which ones are the best Batman villains. Not necessarily best villains overall, although you’re welcome to share your opinions on that, but specifically best villains for Batman. Which ones challenge him and his ideals the most? Which single villain do you personally think is the best for him, and why?