ampclamp is correct, his statement is true for when there is little fuel in tank.
When main tank 1 is full (not below ~1000kg/2000lbs then it doesn't matter which pump s used, as both are suitably submerged.
When centre tank full is available (above minimum quantity for ground use as er your aircraft specification) use CTR fuel instead to avoid an imbalance.
Simple...
FWD FUEL PUMP 2?
Never unless you've got crossed open and AFT FUEL PUMP 1 is selected OFF