DCL is a flawed but talented center forward who's being asked to play a role that doesn't suit him. He's not a target man but has a high defensive work rate and when Ancelotti reduced his role he had his best run of form. It also helped that he had more talent around him then. Dom is better featured in a front 2 or at least a different setup from what Dyche prefers.
Beto is raw and not ready for PL action and maybe never will adjust. But he can be an imposing striker if he learns how to fit the league, although we are still months from learning this. He doesn't appear to have much hold up play and is better running onto balls, which may seem to fit Dyche's counter attacking setup but hasn't worked yet. If he can learn to time his runs he may be a good proper unit up front.
Neither is good enough for what the manager wants to employ, however, but if you have to choose one you choose Dom.