IMO satin for everything exterior, except maybe semigloss on a front door. Thats personal preference. I worked for someone who always had me put satin on the body and semigloss on the trim, and personally, I just dont like it. Nowadays, even decent quality flat paint will hold up about as long as anything else. Semigloss isnt any more washable than satin, if you ask me.
As far as longevity.... on one hand, shinier paints will reflect more sunlight rather than absorb it, so that may add to the longevity, as well as keep it a touch cooler.. On the other hand, when exterior semigloss is near the end of its lifespan, it looks a lot worse than satin or flat, as the worn areas lose sheen and become an eyesore. Ive just noticed exterior repaints, the fascia always looks worse when it was done in semigloss, compared to satin, or even flat. So, personally, I say satin all the way, except maybe the front door.