OP,
You know your state better than us (unless you tell us what your state is), but if you know the norms for the area, it becomes easier to plan.

In NY:
State Route (has a state number): Always has white and yellow lines, usually very good shoulders, almost always 55 mph speed limit. I choose these as last resort.
County Route (has a county number and a name): Always has yellow line, usually has white, shoulders narrower than state routes, and in marginal conditions, evenly split between 45 mph and 55 mph. Usually make for decent riding roads.
Town Route (has a name but no number): Never has a white line, usually has a yellow. No discernible shoulder, rarely 55 mph. Usually they are 35 -45 mph. Usually make for decent riding.

These are the Central NY rules. Figure out which ones apply to your area.