GSO is the safest. EVen though CSO is FDA approved, there is still some concern that since cotton is not considered a food, more harsh chemicals and pesticides can be used and are too small to filter and very difficult to wash off or remove.
GSO is a bi-product mostly from the wine making industry which is grown with stricter guideline as to what chemicals may be used since it is a "food". It also goes through a very thorough cleansing process.