Capital efficiency is one of the most important aspect of trading.
Futures have the edge in capital efficiency when compared to stocks because SPAN margin--the margining system used for futures--incorporates more variables into its calculation.
This causes futures margining to be more efficient and stable across products.
Stocks on the other hand tend to be more variable on the margin per unit of movement that the stock gives you. This is because equity margining does not take into account volatility or price movement.
For capital efficiency, go to futures as your main source of trading as the margining per unit of movement is efficient across all products.