I would definitely go with Pattinson over Hoult. WB is essentially rolling out the red carpet for him with the new Nolan film, and using it to re-introduce him to audiences. It's all clearly meant to have a synergistic effect. Announce Pattinson as one of the leads in the new Nolan film; then announce he is the new Batman. That will drive audiences to the new Nolan film to check him out, and if it's good, will only increase interest in and traffic for the new Batman film.
We see what you're doing, WB. You had my attention. Now, you got my interest.