I'd sort by legroom if the flight search engines offered that information, but it is not available: price is the only discriminator.
Want +3in legroom? For each flight, go to a flight forum and punch in the route to figure out what plane they're flying. Google the airline and that plane to figure out how much legroom is available.
Give up and just fly jetblue and/or southwest, and if they don't go, decline to travel.
1. Flightaware
2. Seatguru
3...
4. Comfortable flying
(Step 3 is becoming a millionaire that flies business class.)