I think most people go with capital gains tax. But honestly I am fine with any.
People hate taxes but i support them. Really. Without taxes, a country like the US will never be good and have a rapid rate of economy development.
Think about taxes as to help our goverments to build the cities, education and future for our children. This will make us more willing to pay taxes and forget about selfish needs.
I dont think so that there is any such governing authority which can impose tax over any of the crypto currency for now as these crypto currencies are decentralized in nature and that they dont come under the rule of any of the government. Government will only be able to impose tax over these crypto currencies at time once the government will declare them as legal currencies.