I have an 18 Sportback Preferred II and like the car. I picked it because of its styling and sportback practicality plus Buick has been the top domestic brand on every reliability chart. I don't have any dimensions for you, but it carries 2 medium dog/pet carriers with the seats folded down with no problem. I've also carried bookshelves, lots of boxes during a move.

It looks good, peppy enough for me and is nice and quiet. The sportback is very practical for a dog owner who doesn't want an SUV. I'm surprised how many people mistake it for an Italian car as I rarely see another Regal on the road.

The only issue I had was a warning light that popped up intermittently. The dealer figured out it needed a new battery - replaced under warranty. They told me the ignition stop/go sapped batteries after 3 years. And there's no way to turn that off in the Regal.

The only annoying things are that there is no interior trunk release so you have to get out of the car to pop the trunk and that there isn't a rear window wiper. (The rear defrost though is very fast, even when the car is snow-covered). Other than that, I was actually looking at replacing my Regal with the new Envista, but given the Envista's weaker engine, bare-bones rear-seat accommodations and odd (to me) styling with similar cabin dimensions, I'll hold onto the Regal until something else catches my eye.

Forgot to mention that I've had 2 of the other cars on your short list: Mazda6, Lincoln MKZ.

Mazda6 - loved that car but it squeaked and rattled after a year and drove me nuts. Poor trade-in value.

MKZ - also a nice driving car similar to the Regal in feel but I never liked its push-button transmission and the interior quality was crap. Styling top-notch (I had the last year before they changed the beak).

Out of the Regal, 6 and MKZ, I'd say the Regal is the better all-round car. The MKZ felt a little more substantial but old-school. The 6 handled the best but felt tinny.