My favorites human characters are:
Paul - Total rockstar. He's got such a professional attitude. Although he was beaten by Ash in the end, I think Paul was genuinely the better trainer.
James - I loved all of team rocket when they were the goofballs of the show. They made me laugh so much. I preferred James to Jesse just because he was the nicer of the two.
May - My favorite female companion. She was the most humble I think.
Brock - My favorite companion of all. He was a little of everything: Funny, smart. A real cool guy. He just tries too hard with the ladies.
And don't make me choose between those 4.