Can't say I would have just the one if money were no object, I'd have a nice selection.
If you were pressing me on just one car then it's got to be something that blends most of my driving so probably a new Mercedes C63 AMG Estate
Money no object though I'd have the best Smart Fortwo '450' Brabus, the A2, a DS4 200THP DSport and the Mercedes C63 Estate.