Which is better - 90 octane no ethanol or 93 octane 10% ethanol

OP: really depends on what your car is tuned to run. If it runs satisfactorily on E10, either keep running it that way, or try adding 4-5 gals to 1/4 tank when you get down that far. The example I'm about to use is like apples to oranges, but at least they're both still fruit...after driving my pickup for several months using midgrade 89 E10 fuel, I fueled up at a station out of town with a non-alcohol blend. Overall, the truck ran fine, but it started pinging little...never did that on the E10 fuels. Now, that being said, we're talking a modern engine with EFI and knock sensors and programmed to adapt for ethanol blended fuels, so it was able to compensate but with slighted performance since timing was readjusted to reduce the spark knock. Long story short, I ran the tank down as far as I could with that fuel and then filled back up with my regular stop.

BLUF: If you're setup to run real gas, you'll be fine, if it's been running good with E10, I'd be measured about how much I put in there and pay close attention to the way it responds, otherwise--go for it