IMO, if it's for a female that wants to pose [assuming the desired effect is related to other peoples opinions of her in the car] I would say the Porsche.

If I saw a woman in a Jag I would assume that she'd borrowed it from her elderly husband/father/insert any type of male over 50 here [delete as appropriate ]. My dad had one to smoke about in a few years ago and yes they are lovely cruisers, they are in fact pretty nice cars when it comes down to it, but he's knocking on the door of 60 and likes to beep his horn at teenage girls

However, if I saw a woman in a Porsche Boxster, I would ask for a go on her tits.