I assume your car has the CVT. In that case, I'd say opt for the lowest RPM you can get away with.
Modern CVT's will load up the engine while keep RPM remarkably low -- if you keep your foot out of it -- which is better for overall economy.
And if the car has a "manual" shift mode (buttons or a different shift gate), consider using it to request even earlier "upshifts" than the default programming gives. That will save even more fuel, especially if you can get to "top gear" sooner and at a lower cruising speed than the default programming would otherwise do.
See: "Short-shifting" a Jeep Patriot & Audi A4 CVT (forcing early "upshift") saves gas
Having said all this, how you use the BRAKE pedal (or
don't use it) has a bigger impact on your overall economy than what you do with the gas pedal (other than on the highway, of course). Food for thought.