It really depends on the planting of the tank. If you have a lot of plants at the front of the tank, I would go with two of those over the tank, but If you mainly plant to have a planted background with a more open front, that would be more ideal.

To put it more simply:
1 light in back means plants will grow up the background
1 light in the front means plants will tend to spread out to the front, or descend from the background
2 lights means maximum growth upwards and outwards