The engineers who designed the engine and the EFI system know more bout engine design in general and your Honda Rebel engine in particular compared to we all in this forum. Not only they designed the system, but they had to test every parameter to make sure they'll have the least amount of warranty claims under normal operating conditions. I would listen to what they recommend.
In my Honda Rebel 1100, they recommend using a fuel with at least 86 octanes and maximum 10% ethanol. In the U.S., the cheapest unleaded gas is 87 E10. Any performance gains from using a higher octane or lower ethanol content will not offset the increased cost. I would recommend everyone to save some money and follow the manufacturer recommendations (unless you are tunning your engine to different parameters, but that's a different story).
The only exception is when the bike will sit unused for more than 30 days. Ethanol is hygroscopic. It adsorbs water (different from absorption) which means it attracts water. That water corrodes metal parts. Ethanol also increases the level of oxygen in the gas, which turns the paraffins and other gasoline molecules into a gel. That gums up the ejectors and other components. In summary, ethanol-containing gas sitting in the bike for more than 30 days is a big no-no. You should add stabilizers or use ethanol-free gas whenever you will not use all the gas in the tank within a 30-days period.