Type of floor to use for a three season porch
Vinyl plank flooring is very durable, attractive, and moves less than wood-based products. It comes in many styles, some of which very convincingly emulate natural wood through color and texture. 

Just this past weekend I helped my brother install some in his home. It had built-in flexible underlayment, was very easy to cut (simple crosscuts are score-and-snap), and looked absolutely beautiful. Seams were dead tight and the product claims complete water resistance. Judging by the fit and feel of the material, I can't say I don't believe them. 

Quality varies with brand, of course. Do your research and read objective reviews.