I've tried nearly all the ones out there and had unsatisfactory results.
Until I tried 'invisible glass' which was on sale at Waxstock 2014. Used with crumpled newspaper it is just stunning. Best thing I've ever used.
White vinegar and newspaper for a basic go.
I really struggled for ages with my windscreen, just couldn't get all the smears off despite trying vinegar, jet wash, fairy, diluted meths, domestic window cleaner, Wynns window foam.
What really, really worked was a tub of furniture leather degreaser ( that we used on an old sofa).. All the smears gone and stayed gone. Needs a bit of elbow grease but it's really done the trick