I view G4 Luffy as stronger than Yami Teach.
Since teach could take WB quakes right to the face I think he wins. He can also easily cancel out Luffys G4 by touching him
Tough call, Luffy showed he can go G4 in an instant and without even having to bite his arms (Oda doesn't give a shit) so the Yami's ability to disable the form won't be as much of an issue as one could think. With G4 Luffy will be tossing Teach around, but Teach can take a good number of blows. He'll still have to be able to keep G4 off his back if he's to win though, a sustained assault will get him. We don't know the true power of the Yami Yami no Mi, he could very well be capable of holding Luffy down with it, like with that move that overpowered Entei. Teach seems like a reasonable match-up with his tankiness and Yami, but it depends on what the Yami is really capable of, which we don't know and by this point never will know as the next Teach we see will be the 2+ years one who has most likely improved significantly with both fruits.
Teach tries pulling him in and gets a King Kong Gun launched at him.
King Kong needs set up you know.
Even 2 seconds matters a lot in battle the higher tier you go.
If Blackbeard can beat Luffy in 20 minutes.