Seeing as how the only person in the world who has reacted favourably to the news that Ben Affleck is going to be the next Batman is Matt Damon, I thought that I might as well ask, who would you have chosen instead?
Put yourself in the shoes of the casting director. The star of the last (a hugely successful with both critics and audiences) trilogy of films has ruled himself out of returning to the cape and cowl, so now you've got to find someone who can play an older more experienced and battle hardened Batman who can stand up to super-humans way above his power range for at least two movies and probably more as the Justice League juggernaut is prepared. Who do you pick?
