I personally can't stand Rain-X. It leaves a slight haze on the windshield, even when applied lightly. I guess I'm just very sensitive to it.
However, I found that I get better results with a clean windshield and good wipers. I prefer ExactFit wipers.
I've cleaned a severely road-greased windshield in the following manner:
1) wash with detergent.
2) clean with a degreaser, rinse thoroughly. Avoid getting the degreaser on the paint.
3) clean using paper towels dampened with Varsol. Make sure this doesn't get on the paint, and avoid rubber seals.
It'* a pain, but I've tried lots of cleaners with no success. The above process worked well.
The only windshield reservoir cleaner that I've ever been happy with is from 20/10.