For 2011 Prius, Everything else being equal, when leaving a red light or speeding up on a freeway is it better for mpg to: 1. Drive in Eco mode, accelerating slowly like a slowpoke to never leave the Right side of the "Eco" area (ie never go into pwr area)? 2. Drive in Eco mode accelerating quickly in "pwr" area? 3. Drive in "normal" mode and accelerate quickly? 4. Something else? Thanks!!!!
Somewhat option #2. Accelerate briskly to get up to desired speed then lift off the throttle then reapply throttle to maintain desired speed. Brisk doesn't mean floor it and it doesn't mean granny foot it. Avoid frequent short trips and do not drive around using EV mode all the time. The Laws of physics will catch up to you otherwise.
I would say you'd want to go somewhat into the power band/bar when accelerating, especially onto the highway. In the end, the amount of gas you burn getting up to speed (on the highway) is secondary to the amount of gas you burn once ON the highway. Keep your speeds down and watch your mileage go up.
What F8L said. It has been proven that brisk acceleration is the way to go. Any "proven" I mean that some of the best Hypermilers use this technique.
About halfway through a recent road trip I switched our ECO button off (after keeping it of more-or-less constantly since purchase last fall). It just seemed like whenever I asked for gas, I had to go back and ask for more, so just to save two trips, LOL. We've gone maybe a bit over tank in normal mode (neither ECO or Power mode): mileage doesn't seem to have suffered. I've heard the AC behaviour is geared to better fuel economy in ECO mode, but other than that... So, sort-of #3, but I'm still quite gentle in accelerating. I'll start backing off the acceleration maybe 5 km/hr below my target speed, just ease up to it. And, as long as there's no one breathing down my neck, I'll stay under the limit, coast to lights, what have you. And if there is someone right behind, I still don't speed, just stay close to the limit: it's safer, better for fuel economy due to less accelerating/deccelerating.