Nothing makes a cabinet look worse than door panels with unattractive grain that runs at weird angles. It pays to be picky about grain direction, even if it means wasting some plywood.
After assembling your door frames without glue, slide them around on the sheet of plywood until they frame attractive panels. Look for symmetrical grain patterns that you can center. Avoid patterns that run off one side.
I try to find grain that resembles mountains or cathedral arches. These A-shaped patterns make doors and cabinets appear taller and more graceful. Tight grain patterns, where the early and late growth is closely spaced, usually look better than patterns with wide grain.
Mark your good-looking panels by tracing around the inside of the door frames. Cut out the traced panels at least 1/2 in. larger on all four sides. Then trim them to fit the frames. Use the ugly plywood that’s left over for jigs or in other places where appearance doesn’t matter.