I would choose two but there isn't much of a difference in meaning. ''Efficient'' and ''possible'' are both adjectives that can modify ''way''. ''Possible'' is also one of the adjectives that is both prepositive and postpositive, meaning that it can go both before or after the noun.

In fact, I literally say ‘most efficient way possible’ in my intro video on my profile here haha and I’m a native.. so..

The 2nd example is more ‘English sounding’.

2nd sentence!!

They are both okay, but the second one sounds way better than the first.