Meh, I haven't voted yet for good reason.
On one hand: Blackbeard is an unknown quantity. He appears to struggle dealing with Luffy in ID, gets owned by Magellan in a heartbeat and even struggles Ace with their battle. But then he is said to have the strength to break necks, ability to cancel fruits on a touch, and to have wounded Shanks and killed a division commander. BB is still more hype than show.
And on the other hand: Magellan is quite possibly the strongest parmecia fruit user we've ever seen. Powerful enough to keep the world's strongest criminals in a state of fear, and send hardened veterens running for their lives. Minus a little blood emerging from his mouth, we have not seen Magellan take much physical damage despite canon fire, Luffy punches and other misc attacks, indicating that, even if you ignore his fruit, he has good tolerance and defensive capabilities. Drawing out a battle against a strong defence is natural, and Magellan is the type that you cannot afford to draw out a battle with.
Yet that said, BB is being set up by Oda as a great villain. The plot side of me says that BB will win the next confrontation between the two (or Shiryuu), but what we've seen still tells me that Magellan is beyond BB's league. Heck, Magellan is top tier and up there with where I'd rate admirals, Yonkou and mid/top tier Shichibukai.