Ethanol free if you can find it, but star tron if you have to use e-10. STA-BIL isn't worth the bottle it comes in IMHO. The BEST thing I have found to do myself is to run the engine out of gas when your done boating. No gas in the carbs, no gas to varnish and plug up the carbs. The problem comes in for 2 strokes if they use oil injection that injects the oil directly into the gas. If yours does this, then your engine has no oil in the fuel when you 1st start it back up after running it out of fuel. If the engine is pre-mixed, then disconnect the fuel line, run it out of fuel, and the next time you want to use it hook the line back up, pump it up, and go. I have done this with my 35HP JOHNSON, and have yet to need to touch the carb since 2003, and it sat for about 5 years not being used.