E
Let's suppose Blackbeard is not the only one person who can eat more than one DFs, and there is a random character who can do that, too.
What two devil fruits would you choose, if you were him? You can eat any DF, canon and non-canon (anime only) but the max is three. Remember, there is 175 DFs and each one of them is unique
It doesn't have to be the strongest combo, it can be the coolest, most creative, weirdest, etc. Whatever you wants.
My opinion is, the strongest combination Hana Hana no Mi, Suke Suke no Mi and Hobi Hobi no Mi, mixed with basic CoA it's basically insta-win against any character. Even if it's PK level.