I owned a Tokina 50-135 for a couple years but don't think I ever owned it at the same time I had a C100. I sold it and bought a Sigma 50-150 and liked that lens a lot better. The Sigma is a lot sharper than the Tokina.
Since I don't own the Tokina anymore I can't directly compare the AF but I remember the AF on the Sigma being faster on the 70D.