User blog comment:TheWiseAnon/Supernovas v, Luffy/@comment-452405-20100727032552

Bounty = Threat to World Government, not strength. Robin's first bounty was what, 79 million? And this was to an 8 year old girl just because she could read some ruins.

I reckon Law's much stronger then he appears, as he showed no hesitation in flipping off Kidd, the guy with the highest bounty there. His Devil Fruit power would also be tricky to get around, as Luffy would have trouble getting to him as that'd mean entering Law's "room".

Bonny, while seemingly physically weak, again her Devil Fruit would be a problem. Then again we don't know much about it, like range of effect, how old/young she can age you or how long it lasts.

Luffy doesn't carry any metal with him, so Kidd shouldn't be an issue for him unless his hand-to-hand is extremely good. Only Zoro, Franky and Brook should have an issue as their weapons are steel, I mean half of Franky's body is steel!

I'd be tempted to say Urouge for his immense strength, but then again Luffy has Gear 3rd to counter him. The same goes for all the other Supernovas, sure they might be able to go toe-to-toe with Luffy at first, but once he activates his Gears things should turn in his favour really quickly, well in theory at least.