Most Logical?

I would say Brock. He was the most knowledgeable of Ash's companions and he had the feeling of a mentor and sage advice giver at least in the first few seasons. He was also much more level headed and mature than Ash and Misty and less rash and impulsive than Ash.

Hmmm... Other than possibly Brock (who I really wouldn't say is all THAT logical since he DID fall for James' story regarding his dying in front of a church in Holy Matrimony, which even a kindergartner can see through the lie. And don't get me started on his womanizing gag.), the only other character I can think of who is very logical is Misty. She did come up with the plan to get out of the St. Anne, and she did solve most of the riddles on Cinnabar Island. Not to mention she was at least smart enough to not fall for James' church story for very obvious reasons ("JAMES IS STANDING RIGHT HERE!").

I would say Brock would be the best answer to this question. He seemed like he was the best one to keep things in order and do what was the right thing to do. He also had this tendency to realize when something was not quite right, example: "I should've known there was something fishy about them (Team Rocket disguised as Vikings) besides the way they smell!"