To me, "understand the least" has nothing to do with "dislike the most" or "think I'm the most unlike." It means the character whose head I can't getting into. Whose eyes I can't see through no matter how I try, if that makes sense. As a writer, I have spent years learning to see through the eyes of others, and I can do that for most characters in most things. But not all. Some characters block me, and I can never feel like I fully understand them.
So in the LOTR trilogy, the character I understand the least is Frodo Baggins.
Yeah, I cerebrally understand what's going on with him. I know how he works, why he does the things he does, what's going on with him at the various stages. But I never feel like I know him the way I do the others. Even the bad characters, like Denethor and Grima and Saruman, I can understand more fully than Frodo.
The best way I can think of to explain it right now is that it's like the difference between seeing a picture of a chocolate chip cookie and actually eating a chocolate chip cookie. (Not coincidentally, I baked said cookies today.) I can see the picture of the cookie and imagine what it would taste like and smell like and feel like in my mouth, but it's not the same as actually taking a bite of a cookie. I hope that makes some sense.
Do I wish I understood Frodo better? Yes, I do. But I've come to accept that there are some characters I just will never fully "get."