Air with regular masking tape. I will give the blue painters tape a try sometime, but for the present I have a good supply of 2" masking tape.
Btw, I have used air for more than 20 years. The only grips I have every had some issues removing (that are worth while) have been the early model Winn grips. Air is great when you want to remove grips and save them or fine tune your grips with tape..