I do not want to deal with a world where I have to decide, Sophie's Choice style whether I love Blood Simple or No Country for Old Men more. That way lies madness.
Blood Simple, because of the amazing DVD commentary.
As we can observe on your chart John Turturro (T) is clearly not necessary as he is never seen in any film that does not feature John Goodman (G) or Steve Buscemi (B) while both of them appear in a greater number of awesome-level films.
Quality over quantity: Turturro plays an important role in 3 of the 4 films, Buscemi only in Fargo (even in Lebowski he's only slightly more significant than Turturro). I'd go Goodman > Turturro > Buscemi, but Turturro is the common denominator in my top three.
Burn After Reading I could see putting in the same category as O Brother, but I felt that it was much flatter in general. It wasn't bad, it just wasn't very good and it needs to be dropped into it's own sort of purgatory for that.
Clearly they put a lot more effort into O Brother than Burn After Reading, but a few scenes that miss their mark and make it harder to watch for me. But from a purely technical perspective obviously O Brother is far superior.
I hate Tom Hanks. I have always hated Tom Hanks. I always will hate Tom Hanks.
I hate Tom Hanks. I also hate Nicholas Cage, yet Raising Arizona is near the top.
The bottom line is the Coens manage to get great performances out of both.
The Man Who Wasn't There is given extra preference because of the gorgeous B&W cinematography and because the Coens are going back and giving us an almost straight noir film without their additional trappings and modifications like we see in Fargo (their third most noirish going by classical conventions).
I just thought it got derailed towards the end. Like O Brother, I punish it for not being as good as it could have been. Perhaps my expectations were too high for both, based on the trailers. Also, Tony Shalhoub's character should have been utilized more.
Ultimately your rating is interesting to me as it seems you prefer their widely-praised mid-period works (Barton Fink, Miller's Crossing), then their comedies, and lastly their more direct noirs. Interesting even if I disagree.
Miller's Crossing is one of the best films ever made. I think the plot is too intricate and some of the dialogue is too subtle for people to really appreciate it after just one viewing.