I would say that the best way to fund an online casino out of those three options is to use Bitcoin for a number of reasons. The most important reason is because of the anonymity involved with the cryptocurrency. When you make a deposit using Bitcoin, you do not have to give any personal information (such as name, address, SSN) that could possibly be stolen. That makes the options of depositing via PayPal or credit cards risky, and there could also be chargebacks involved with those two options if you are playing from a country that is not allowed.