Well, for me, there are a wide variety of things that I have to consider when looking for a free car. Part of it comes down to having to live with it day-to-day, actually driving it, and what kind of practical uses it could have. In these kinds of circumstances, I'm often lead down two separate paths:
1) A moderate or large sized, V8 sedan. Preferably American or English, which narrows those choices down considerably
2) A "practical" sports car, usually having four seats, a boot that can carry things, coming from a brand that knows that the hell they're doing
In the case of the first path, my choices are whittled down almost immediately to the Dodge Charger/Chrysler 300, the Pontiac G8 GXP, the Chevrolet SS, or the Jaguar XF and XJ. In that group, I'd have to throw out the Mopars almost immediately, they're just not all that great in terms of performance and quality. The personality just isn't there either. Between the G8 GXP and the SS, well, it really depends on the kind of creature comforts you want, and whether or not you need that six-speed manual. Among the Americans, I'd have to say that the Chevrolet SS gets the nod here.
For the Brits, well, it's a matter of size and generation. As much as I love the current XF, it still hasn't clung onto my heartstrings like some of the other Jaguars have. The same can be said for the XJ, where in this situation, I have to say that I'd still prefer it's predecessor to the current model. I'm a madman, clearly. But, the 2014 model is pulling on those heartstrings again...
Between the 2014 Jaguar XJR and the 2014 Chevrolet SS, in the end, I think I'd have to go with the Jaguar.
On the flip side, well, I feel as though there are only two options; The Lotus Evora S and the Porsche 911 Carerra 4S (991). The Lotus just looks and feels great, even if the back seats are useless. The Porsche is a Porsche, and that means that you have to expect a Porsche... A sports car that will probably run forever if you take care of it. Also, useless back seats.
Between the two, honestly, it has to tilt in favor of the Porsche almost immediately. Even in lesser Carerra 4 form, it just makes more sense as a day-to-day vehicle. Throw a roof rack on it, give it a set of solid all-seasons, and there isn't much that'll stop it when you're trekking cross-country in any weather condition. A bunch of different options can really make it your own. Nothing wrong with that.
So, Jaguar XJR vs Porsche 911 Carerra 4S. That's a pretty big leap to make between the two of them. Very different ends of the performance spectrum, but each would likely produce similar numbers (in a weird way). The Jaguar is beautiful, it sure as hell is substantial, but in the end, I'd have to go with the Porsche. It's just the right way to go.