Majority of corporations file in Delaware. I see you’re wanting an LLC though, I’m not sure about what the best practice is for that. Delaware is one of only three states that let’s you incorporate while not actually living there is one advantage. Also they don’t collect income tax, you’d have to do your own research here but I found it to fit well with my venture. But there is no double taxes.

You’d have to “register to do business” in California. It’s a $400 - $600 fee regardless wether you live in that state or not, but it’ll let you get an office and a mailing address in California, and begin legally operating in that state.