One Piece has a lot of lovable idiots, but there are plenty of smart ones too. Who do you think is the smartest?
But then there are various definitions of smartest. It could be measured by different means, like:
Book smarts (as in knowledgeable) I will say Robin and those Ohara historians.
Nami wins her fights through intelligence (and a bit of luck), and her weather knowledge is godly. Sanji is shown to be very smart from the way he saves the day(s) (provided there are no women around).
Franky, CC and Dr Vegapunk are pretty impressive too, but I don't know how to catagorise them.
Luffy can be gasp actually quite clever sometimes during fights, like how he came up with the gears and stuff.
In terms of planning I would leave it blank, because I would answer Crocodile, and he's my favourite character so I am afraid that my judgement will be clouded. :ninja:
Those who discuss power levels here will be chased by psycho tortoises for an eternity.
But seriously, I made this thread to know who people think has the highest intelligence, not highest fighting power in OP, so erm, I hope no power level discussions appear here.