Maker's Mark actually promotes the fact that everything they do is intended to eliminate bitterness from their whiskey. If not-bitter is primarily what you are looking for, Maker's is hard to beat.
Col. Charles K. "Crotchety" Cowdery
"Whiskey Don't Keep."
I agree with everything you said here. Most good bourbons are not what I would call bitter. Also, you mention Michters American Whiskey. Not only is that not bitter but isn't that the sweetest whiskey you ever had? So sweet it's unusual. I've never had another whiskey that sweet to this day.