Originally posted by NemeBro
Luffy adds far more to Goku than any of the others.The only thing Naruto adds to Goku that he did not already possess is a healing factor, and Ichigo adds nothing I can think of to Goku. The increase in power level would be completely inconsequential.
Luffy adds precog, the ability to further enhance his physical strength and defense, and most importantly, virtual immunity to blunt force attacks and stretching. See, the thing is, Ichigo and Naruto's amps are linear, they add to his strength. But Haki and Gears multiplies Goku's already incredible power.
For starters, Naruto's "power level" as it were is going to be above Luffy's. This will put the Naruto form above the Luffy form as we all know power levels are the only thing that matters.
No but seriously, Sage Mode and Kyuubi Mode both have abilities similar to that of Mantra and stat enhancements. The only thing worth noting there is immunity to blunt force trauma, which is nothing new for Goku to fight(see Buu). This fight will have ki blasts, which will nullify whatever advantages Luffy might give Goku.
Meanwhile, Naruto has two thousand clones that all, technically, have a higher power level. And the strongest technique here: the substitution jutsu.