Proper light intensity is more important than spectrum for the different stages of growth.
Providing you are meeting this.
A blue dominant spectrum will keep the node spacing tighter giving more compact growth generally favored for veg and stretch.
A more red dominant spectrum is favored for bud development and will cause longer node spacing or stretching in veg.
Depending on genetics you may want one or the other or both.
Generally I would say both but in doing so you will need to raise the light more in earlier stages of growth to do so.
Often people just use the blue to keep stretching down and keep a lower intensity.
So either blue or both for veg and both in flower. If not using both in flower generally you will not meet the ideal intensity for flower.