Even though Superman is my favorite and Batman is the best book in my opinion, the Flash goes to the top of read pile every time. It's the most fun book out there right now and not only have the stories been great, the art is just spectacular.
For me it's between Aquaman and Batman. Honestly I'm not even a big Aquaman fan and that's saying something about how good and consistent that book has been. Especially since I'm a big Batman fan and I put Aquaman right up there with Bats title. Green Arrow has been great since Lemire took over also.