When there is no testable physical difference between hypotheses, we want to use the one that makes it easiest to make the correct prediction.

Yes, we want to use the hypothesis that is easiest to use. But if we use it, does that commit us to 'believing' in it? In the case of no testable physical difference between hypotheses, I propose that someone has no obligation to believe (or admit they believe) that particular theory instead of another one with the same predictions.

I enthusiastically propose that we say we 'have' a belief only when we use or apply a belief for which there is an empirical difference in the predictions of the belief compared to the non-belief. Alternatively, we can use some other word instead of belief, that will serve to carry this more relevant distinction.

(Later: I realize this comment is actually directed at cousin_it, since he was the one that wrote, 'your degree of belief in (prior probability of) a hypothesis should not depend on how clearly it allows you to think'. I also think I may have reiterated what Vladimir_Nesov wrote here.)