Lea,
I have stopped buying the new bobbins for my old machines as some of them just aren't made well. I've been fortunate to find ebay auctions for original Singer bobbins. I frequently use 3 Singer treadles: A 201k and it uses the class 66 bobbins and a 237 and 15-90, the last 2 both use class 15 bobbins. Some of the new Singer featherweight bobbins are horrible, they're not quite round and had one get stuck in my bobbin case.
So for me the answer is only original bobbins.
(sorry this was so long).
Sharon W. in Texas