In my own opinion, this is how cars should be parked in Singapore. This refers to only to Reverse Parking.
Always park leftmost to the line. Driver has more space on the right. Passengers at the back can all use the right-back door. Front passenger can be let out before parking, and in after parking. Don't worry about the car parked on your left because if he does the same, he will have enough space to come out of his car and that would create space for your front passenger as well. We should always park leftmost to the line to get the maximum open door space for not only ourselves, but for the 2 cars parked next to us and everyone should be happy.
Although if everyone parked in the centre the same can be achieved, but this method guarantees that you will have control of getting the maximum amount of space.