Worst how? Morally, it's Todd, Gus, and Walter shoot to the top.
In terms of which character did I enjoy the least? Easily Skyler. It's not so much that she didn't bring anything to the show, but more that the little she does bring to the show is just to enhance other characters.
That's how I felt when watching the show, then after watching Ozarks, it pretty much solidified it for me.