Well, Franky was always breathing up Sanji's neck.
When it comes to combat abilities Franky always had most stats above Sanji.
However, Franky has been kept out of fights mostly, just like Robin.
It's not a coincidence, if Oda unleashes those two, they can easily overshadow Sanji.
Well as far as we know there's no established hiearchy, this isn't like enies lobby ,Alabasta where the characters had ranks and power levels. So until Oda gives us bounty or straight up says 1 topi roppo is stronger than the other we have to assume their all on a similar level. Anything else is honestly speculation. Since we have no hierarchy right now The Difficulty in which a tobi roppo is taken care of is more impressive than which of them is actually defeated.
Papa Franku is already the most useful SHP. So this is a no brainer.
My guy protected Zori from bullets since he knew nails hurt him bad.
Even stood in front of Btch Mom to shoot her, but alas, he once again need to save his useless crewmates from some scrub numbers. tldr Life or death does not work on Big Papa