I'm with Alex.
That said, in California it is legal to share lanes, essentially because it's not illegal to do so. It's not legal to ride on the shoulder, and it's not legal to cross the double-yellow to pass. So on a one-lane road that is wide enough to share safely, given the choices you list, the safer option is to be on the right side of traffic, but still within the lane. But - it's unexpected by car drivers, and wouldn't be something I'd generally consider unless traffic was completely stopped.
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