I just want to beat Trump. I think Biden's been a fine president and is a good man, but I have no specific loyalty to him nor do I think he "deserves" anything.
I think the odds of him running a "old moment"-free campaign for the next four months are next to nil. You can whine and complain that coverage of Biden is different than coverage of Trump and you'd be absolutely right, but that's as useful as a basketball coach complaining in 2024 that some shots are worth 3 points while others are only worth 2. It's the rules of the game, like it or not, and you must adjust accordingly. I also think "will this guy survive the next four years?" is a perfectly valid question for voters to ask themselves and those just waving off the voters concerned by it have a poor understanding of the American electorate as a whole.
Bottom line: If I was a betting man, Trump beats both. I think the best case for the Biden campaign is a slow, boring trudge over the next four months that results in a squeaker of a victory. Worst case, he has some moments where his age is evident and the bottom absolutely falls out of his campaign. For Kamala, I think the worst case is similar to Joe, but the best case is completely unknown. Sometimes, all a team needs is a coaching change midseason to give everyone a shot in the arm and then the positivity snowballs. And sometimes a team switches coaches and absolutely nothing changes.
I don't know the answer, but I feel like I know exactly what will happen if Joe stays in and it worries me. For that reason, I would choose the mystery box of Kamala... but I understand why this is a tough call and I would much rather be on the other side of the aisle at this time.
(Note: The absolute certain way to lose would be for Joe to be replaced but for him to publicly air his grievances with the decision. It CANNOT appear like it was "taken" from him, even if that's the reality. Without at least an appearance of buy-in from Biden, this conversation is moot.)