How fast or slow should you do a rep to achieve the maxium amount of muscle growth and strength gain?

Everybody tells me different things...

1,2,3 down, power it up
1,2,3 down, 1,2,3 up
1 down, 1 up

for me, it depends on the weight.. if it's light, power it up and down. but if it's heavy it's like 1,2,3,4 up, 1,2, down