I bought the Stinger GT2 for a variety of reasons: beauty, comfort, power, and my trust in the Kia brand.
My favorite aspects so far are pretty much all of those things.
The Stinger is a beauty. In my opinion, to get something that looks sharper would cost me far more than the Stinger cost. I know a lot of people care less about the 'appearance' than they do about handling, performance, etc, but for me, I refuse to buy an ugly car - or a car that doesn't aesthetically move me. This car -moves- me. From the time I saw the first images, it's haunted me for months, even worse than I saw the first images of the re-designed Optima.
The comfort level makes me feel like I am driving a luxury sedan - but a luxury sedan that I can actually -afford-. I admit, every time I drive it, I feel like I've 'cheated the system' or something, to have a ride so comfortable. A lot of times I feel like I am in a car 'above my pay grade', but then I smile because I know I'm not. If I had one complaint about my Optima, it was that the seats were a little unforgiving. The Stinger's seats are -superb-.
I've owned pony cars, but the power of this car is just beastly - with two fewer cylinders, two more doors, and a functional backseat. I'm not looking for McLaren-type power, but for the price-range, the power provided by the V6 is just wonderful. The first time I took my wife for a drive in it, she had no idea what it was capable of. I took off at a light, tossing her back into her seat with a squeal. She asked me to make sure my life insurance was up to date because she's fairly certain I am going to fly off a bridge at some point.
I bought a 2011 Optima new from the dealer back after Kia had just started to 'rebrand' itself. I took a gamble, but felt confident with Kia's excellent warranty, and loving the look of the Optima. I've had that car for 7 years (and still have it), and it has been the most rock-solid vehicle I've ever owned. This gives me even more confidence with the Stinger.
Of course we could go on and on about the add-ons: the auto lift and close tailgate, the vented and heated seats, the info/nav system, the excellent brakes, auto-folding side mirrors and so on, as well as the HUD which I am already completely addicted to. But the above points were the most important points for me, and on all of those items Kia has scored an A++ in my eyes.
-Tim