Even if all three were the same price, I would still take the Slingshot. Looks like it would be a blast. The Morgan seems like it needs fatter tires, although the video seems like it does just fine on the corners. I've ridden two different Spiders. Was not real impressed. Seemed cheap. Fun though.
The Spyder is the only one resembling a motorcycle.
I would prefer it mostly because of that and that the seat height is higher providing better visibility for the rider and especially more visibility for the cage drivers on the roadways. I would NOT wish to be involved in even a minor side impact, or any other for that matter, in the Polaris or Morgan while being trapped inside those vehicles.
Here the Spyder technically IS considered a motorcycle because the rider straddles the engine.
Same as a Harley, Goldwing or Triumph trike, just a reverse trike.