Manan

Well, Job boy was moreover THE ONE who had setup the game (One Piece) for other pirates to find and finish it... Moreover Joy Boy was like a Dungeon Master, who had set up the One Piece and all the challenges and others were just players... And one of the most clever and strongest player/pirate was Gold D. Rodger so he got the title...

I think... Monkey D. Garp... If not stronger but had haki at the level of Rodger at that point of time... Garp may even be stronger than Rodger now as we know in terms of haki... And if we talk about it at that time... Garp had holded future "gonna-be" Yonkos and Emperors like Kaido and Whitebeard as Rodger fought against Rocks...