Most comfortable? Canada. Seems like they take driving a little more seriously there. In the U. S., California is fine. Lane splitting is legal, drivers mostly competent and attentive, cops are about the right mix between lenient and slapping a ticket on you when deserve it. Even in places like L. A. I felt comfortable, even lane splitting with bags on. CA has its problems, but I like riding there. That obviously doesn’t match your experience, but I sadly haven’t ridden down to CA in probably three or four years. I also tend to kind of stay away from the Bay Area on the bike.
A lot of southern states are good, like North Carolina or Tennessee. Good mountain roads, reasonable drivers. And believe it or not, I’ve like riding in New York City. Don’t let the bike out of your sight lest it be stolen (I am dead serious about that unless you have some serious locking equipment). Obnoxious drivers, sure, but competent and it’s almost as if everyone knows that if we don’t cooperate at least a little, nobody’s getting home tonight. All of this of course is one giant sweeping generalization, so no one need trot out their personal list of exceptions.
But Seattle? I fucking hate driving in Seattle. It’s as if every single driver is sixteen years old on their learner’s permit with two months behind the wheel. There’s a reason one of the topics of the very first Portlandia episodes dealt with driving in the PNW.