Based on your heroes, I’d advise on using Tarlak, Wilbur, Falcon, GM and Zimkitha.
Wilbur’s defense down will considerably out weigh taking a hero with a higher attack value. Stacked with Falcon’s elemental defense down and Tarlaks attack boost and you should start to see some serious damage.
I’d bench Puss simply because speed is everything for scoring those big titan hits and his minions will slow you down (unless you keep him for tile damage but don’t use his special to avoid the minion delay).
Another option is Scarlett in place of Zimkitha. She has 767 attack value when max level and as a season 1 4* she is fairly easy to get. Wilbur’s share received damage and her attack down will mean she can survive even against pretty high level titans.