coplanar waveguide vs microstrip for gnss and cellular?
'Better' and 'most efficient' are not words that are useful to use.

Both microstrip and coplanar have their own advantages and disadvantages. However, often it's the integration with the significant ICs on the board that's the key factor. Some ICs have pinouts that invite connection directly to coplanar (with a GND-sig-GND set of pins) or microstrip (with a ground pad and a single signal pin).

Coplanar makes it easier to use shunt components, they just go straight across the gap without the need for vias. However, the need for balance between the two grounds needs them tacked to each other sufficiently often. The top surface grounds can crowd the available real estate.

Coplanar-with-ground is a hybrid of the two which can be used to transition between them.

There's little significant difference between the attenuation constant or dispersion of the two.