To list which additive is the best for E10 gasoline would be doing an injustice to the sheer number of additives there are out there on the market. Most of them are completely useless in E10 because the majority of them contain alcohol or an extremely strong solvent. Instead, to prevent damage from E10 it is important to follow simple precautions such as replacing the fuel often, testing for correct ethanol % upon purchase and installing a decent sized (10 micron or better) water separating filter. However, if all else fails, I'd recommend using an additive such as Eth-Guard to greatly decrease the damage caused by e10 fuels.
To view a list of common additives and how safe they are in E10 fuel visit www.e10gasadditives.com/fuel_additive_list.html
Eth-Guard is safe in all engines and contains no harmful ingredients. It will increase the energy of the fuel, lubricate the fuel system and prevent phase separation in most applications. Generally, additives are not necessary if simple precautions are taken but if you find yourself in a bad situation, Eth-Guard is a great product to use for most ethanol problems.
To view Eth-Guard please visit: www.e10gasadditives.com/product_ethguard.html