All right, all right--no matter WHO was the 3rd Stooge after Shemp's death, he would be a poor substitute unless they could've gotten Buddy Hackett, which would've been interesting...not necessarily better, because either he would've been a "Curly Clone", or something similar.
In response to the Joe-era shorts "sux balls," I tend to think that they were already heading that way, even if Shemp had lived. Lest I repeat stuff we all know, dwindling budgets, etc. had a way of effecting the quality of the shorts.
As far as the worst, I would have to say "Beer Barrel Polecats" simply because of the sheer stupidity of even THINKING of using that amount of stock footage. Curly's health problems had been dealt with successfully in shorts such as "Three Loan Wolves" and "Three Little Pirates", so there was little need to slap together what could've been a great short (the beginning is quite funny) that only needed more material...new material. What resulted was a poorly matched mishmash of young, vibrant Curly/older, ill Curly that made no sense.