The Williams ball looks good to me. As for the Mantle, I'd have to agree with the autopen conclusion. You can see the machine stuttering through the signature.
As others have pointed out COAs are worthless especially when they're not tied to a major TPA.
Is that seal on the Mantle COA flat or an actual separate seal on top of the COA? It certainly looks like a photocopy job.
Mantle could also be a forger's first attempt. I have the same photo (if yours is 8x10) and the signature looks like a forgery with stop, start points. Yours is much more hesitant. Possibly yours was the first few attempts and he got a little better by time he got to mine. Because it does appear same person signed both.