Depends on the type of smartest you're talking about.
Book smart / educated would more than likely be Vegapunk. Franky's probably high up there as well at least in the field of engineering. Judge too.
Street smart / tactics would likely be Teach. Usopp is a strong contender in this field as well for despite lacking the ability to execute at a high strength he formulated a master plan to battle Luffy.
3. shanks cos the red hair pirates is the hardest to infiltrate according to the world goverment
4. luffy idk if its instinct or not but everytime he decided anything it doesnt betray him in the end
I don't agree. Judge was foolish enough that he walked into BM's trap. Not to forget he gave up on Sanji even tho he basically experimented on all his kids. It doesn't matter if he was a failure in his eyes but he can't let his experiment to walk freely. There are other scientists who could have captured Sanji n continued with the experiment or try to figure out what Judge was doing. So I don't agree with him being so high.