Look at it this way: The reason Matt's Big Bird sounds like it does now is because, he has to keep the illusion that Big Bird's still played by one person. Once Caroll's done completely, Matt's Big Bird will sound a lot better. When he sang in this special, it was great. He didn't even need auto-tune like Caroll needed in the Meet Julia episode.As for the voices, I would still take Caroll's over Vogel. I don't think Vogel is right for Big Bird anymore. Caroll needs a new understudy. Vogel's BB is too deep and nasally to the point that it's essentially an entirely different character. Even Vogel has acknowledged the fact that the two sound very different and has stated that his Big Bird is not Caroll's Big Bird. When Matt Vogel was younger he could do the voice, but now it just sounds too rubbery, deep, nasally and cartoonish (if that makes sense.)
I think Jacobsen does a good Oscar, but I'm sorry, I don't buy Vogel as Big Bird. It doesn't feel like the character should feel. Feels more like Barney and less like a 6 year old.
Perhaps Noel Macneal or Peter Linz? (who have both performed Big Bird when Spinney and Vogel were not available.)