Everyone loves on Heath Ledger's Joker, but Jack was much more true to the cartoon/comic character of at least my youth.
Batman has gotten darker as time went along. Heath's performance was a sign of the times, 20 years later. Both were good performances but I liked Jack's better because it's superheros in capes, it's supposed to be a bit cheesy and comical. If you want more true to life comics ... Punisher should be more your go to movie / comic. Batman wears a cape... who does that? That makes it very difficult to blend in to do real detective work. That's a fantasy land and fun and playing it over the top and a bit comical like Jack was just spot on for me.
Heath did bring a whole new angle. I can appreciate both for sure.
But... Best Batman, is Keaton, no doubt though, no matter the year.