What will they cost?

Let’s address the elephant in the room first: purchase price. Or, more specifically, the purchase price of the 911. At more than double the cost of the other cars here, its price is in a different league. Of those two, the 6 Series Convertible just pips the SL to be the cheapest of the three.

The reason for the Porsche’s dramatically inflated price is its vastly higher resale value. That does translate as a used purchase – in other words, as a percentage, the proportion of your outlay that you’ll get back when the time comes to sell on will be greater.

However, in cash terms, that still means you’ll lose less money on either of the other two cars, simply because they haven’t got anywhere near as much value to lose in the first place. Even if the 6 Series Convertible was to lose half of its value in any given period, for example, you’d still lose less hard cash on it than you would on the 911 if it lost a quarter of its value over the course of the same amount of time.

The bad news for the 911 doesn’t stop there, mind you. It also has the highest fuel consumption and the highest tax of the three cars, and servicing isn’t cheap either, although the SL will probably cost you slightly more to keep maintained, as Mercedes dealers don’t offer a fixed-price service option for older cars.

All of which leaves the 911 looking like a particularly expensive option. By contrast, it’s the 6 Series Convertible that works out the cheapest, with the lowest initial purchase price, the best fuel economy, the cheapest tax bills and the least onerous servicing cost. The SL, meanwhile, slots in somewhere between the two, though its high service cost and fuel consumption mean it leans more toward the Porsche than the BMW.