I've got a X100D and a P3D, I absolutely adore both cars. The X is definitely more comfortable obviously and super versatile. The 3 is a great all around car, it can do anything; its a supercar, a great commuter, a computer, and drives itself. but I'm actually second guessing buying the 3 instead of the S. The major reason is I'm coming from a mazdaspeed3 hatchback and a bmw i3, both of which are hatchbacks. The mazdaspeed especially had a ginormous cargo space for a small car; I've even loaded up dishwashers in it. no problem. I've seen all the model 3 videos before buying and thought the rear sedan opening was large enough.
Anyways, with christmas here, I went to put a large giftbox in the back of the 3, I was sure the box wasn't "that big" and it ended up not fitting through the rear opening..... Not a dealbreaker; but frustrating because the space was actually there in the trunk; just couldn't use it. So a Model S with its hatchback opening became a bit more tempting after this experience.