Placement of signal, power and ground lines within a ribbon cable
Interspersed signals with grounds or rails is best for EMI and crosstalk purposes, so your option 1 is better here.

However, in your example you have seven ground wires and only one wire for each power rail. Assuming your signals are mostly logic level, i.e. 5V rail, it would be preferable to reduce the ground lines to four and add three more 5V lines. This will help balance the return current paths for both signal levels.







simulate this circuit &ndash; Schematic created using CircuitLab

Note, with your current setup, when the signal is high the return current is through the shared grounds, when it is low, the return current is through the single wire. Add more signals and the single wire must share all those signals and noise will be seven times more significant on the rail wire.

If the other rails are driving significant currents you should also increase their counts appropriately to try and balance the currents over the available wires.

In addition, as analogsystemsrf mentioned, if the cable is of any appreciable length, it is prudent to slow down the edges of logic signals passed along the cable. Your signals may be low frequencies, but those digital edges are not.