What to use for washer fluid?

Plain old blue Washer Fluid.
When selling it, among other automotive fluids, it was referred to as "G.O.B." for Good Old Blue.

When I was driving 1000 miles a week in the salty northeast, I loved the Rain-X Orange fluid. I'd use two gallons a week, at most. With G.O.B., I'd use at least two gallons a day.