I don't think Affleck is necessarily the best Batman in terms of performance, but in terms of writing and backstory I think he is without a doubt the most interesting and compelling version of Batman we've ever seen on the big screen.

Personally I hate superhero origin stories and roll my eyes every time Batman, Superman or Spiderman is remade and we have to sit through the god damn origin story again, as if nobody in the world knows their origin story already. One of the best quotes I ever heard was, "There's 2 origin stories that never need to be retold again; Jesus and Superman". At this point I would extend those to Batman and Spiderman as well.

Its just so great that we got to just pop right into this universe where Batman already exists and has existed for 20 years with all the backstory and heartbreak that comes with that. Having a history with the Joker with a dead Robin that we've only seen glimpses of was a brilliant storytelling choice. It makes me more interested, it makes me want to find out more, it makes me want to line up and watch the next installment.