I have no idea how you don't tear your ears out listening to ANY dubbed anime. I know I'm likelier to be much pickier then the average watcher as I've been involved in film audio-post production, but it really is just terrible in general.
And I don't blame them at all, it's a very very expensive task to localise Japanese to English well, and they probably don't make enough money on English versions to justify spending a significant amount on it. I can pretty much picture them sitting in the studio listening to a terrible take of dialogue, but one that finally fits the length required to sync with the scene, looking at the clock on the wall and going *sigh* 'that will have to do'. I've been there.
You could say the dub is 'fantastic' compared to the majority of animes, but in and of itself I would struggle to say 'barely acceptable' in terms of post-production quality.
EDIT:
I also tried to watch Cowboy Bebop in English. In my experience you would need to replace the word 'best' with something like 'most acceptable'.