Most people would say that (c) is the correct choice, but I suspect that in practice, the actual split may well be 40% a, 40% b and 20% c.
An extreme example of some choosing box A was Frank Marshall in the 1903 Monte Carlo tournament. Although he finished slightly below 50%, he decided to have some fun against possibly the most famous 'back marker' in tournament history. This was the event where Charles Paul Narcisse Moreau (known to chess history as Colonel Moreau) scored 0/26, losing all his games to the other 13 competitors. While Marshall was known for his attacking play, this game saw it taken to the extreme, playing a Muzio Gambit, offering two pieces within the first 8 moves. The unlucky Moreau was doing OK until move 16, where Bc6 turned out to be the losing move, as the pin down the d file resulted in material lose.
Marshall,Frank James - Moreau,C [C37]
Monte Carlo Monte Carlo (23), 13.03.1903