Does anyone have any advice on painting a wooden porch floor?

I've sanded ALL the old paint off. Bare wood, either pine or fir (mixed, from repairs and such).

What's the best and most durable coating?

Thanks,
Stew

Try a no-skid paint. It works well when the porch is properly primed. Also there is a concrete primer that works in conjunction the no-skid paint.
After priming the bare wood with latex or oil based primer, "prime" the primer with this concrete primer (goes on milkey color and dries clear). Then paint on the no-skid paint.

The most durable paint you can use will be a oil base paint, the no skid paint is fine, it does have a grit to it, kind of like sand, I think it is silicone beads though not for sure,

Usually we just use high gloss oil for the floors usually gray.
Most importantly you do need to prime this before you paint