While I think that it would be extremely interesting to know the truth behind what happened to the Britannic once and for all, I think, like anything, it's near on impossible to prove one way or another after almost a century and after all those who bore witness to it have long passed on.
Then again, isn't that half the thrill of it, trying to solve the unsolveable?
Opinion has always been divided between a mine or a torpedo. Personally I believe it was a mine but that's not based on anything other than guesswork.
Cheers,
Adam.