whats more power,bec or receiver battery running steering

[BrianG]

A BEC, UBEC, or receiver pack will not affect your main motor speed in any way. Your servo speed/power will be better with higher voltage, so a receiver pack may be the way to go since the voltage is usually at 6v or higher. Also, a receiver pack will slightly increase runtime since your main battery won't have to provide power to a BEC/UBEC, but the pack will be something else you have to charge.

As far as wiring a BEC/UBEC; it's the same as any other: Hook the input wires to your batteries and the output wires go to the battery port on your receiver. For a very basic wiring view, you can check this out - just select the BEC option you want to use...