Here's a quote from the southwest website:
"Southwest Airlines Ticketless Customers, who are not checking luggage, may now check in for their flight and receive their boarding pass and Rapid Rewards credit at the Skycap Podium, Ticket Counter, Gate or new RAPID CHECK-IN Kiosk."
From what I was told by a representative and by what I read on their website, you can only use the rapid check-in kiosk if you are not checking luggage.
If you are checking luggage, I've found the most efficient way for my family is to check our luggage curbside with a skycap. When we return our rental car at MCO we go up and do curbside checkin first and then return the car. You get the boarding passes from the skycaps. We've always gotten there 1 and 1/2 hrs. to 2 hours ahead of time and gotten A passes. We gate check our son's stroller and carry his carseat on board.