The odd one
Dont laugh...it has an effect!
If you are flying east over the equator, your relative speed, to a point in space, is your GS of say 480kts and earths rotational speed of 900kts giving a total speed of almost 1400kts...flying west it is around 400kts. Apparently it gives a total differential of almost 0.6% of fuel burn between the two directions, all else being equal!