I usually use ITA Matrix > Expedia (which uses the engine, I think) > Orbitz (if it has more segments than Expedia can handle — this also uses ITA's engine). F

I usually use ITA Matrix > Expedia (which uses the engine, I think) > Orbitz (if it has more segments than Expedia can handle — this also uses ITA's engine). For low-cost/budget flights around Southeast Asia, I just use Skyscanner.