what to use for cleaning?
I use straight window cleaner (take your pick). I think anything with a slight amonia or rubbing alcohol content works fine.
I would agree that the towel or rag you use makes a big difference when it comes to streaking.
To finish things off I use a synthetic wax/polish to remove all haze and spider web looking scratches. The synthetic waxes don't have petroleum in them and reduce smudges.