It all varies from airline to airline.
You generally get more on longhaul than if you are on shorthaul because the trips are longer. But - if you work for Virgin atlantic as main crew you earn the same as BA shorthaul, so you see it depends on the company.
Obviously pay goes up as you work through the ranks, but if you join an airline you'll find that people who have been there for a long time are on old contracts and are earning lot more than you but are doing the same job, as airlines are eroding contracts and pay more and more.
At the end of the day if cash is king then longhaul BA out of LHR is where you want to be.
Hope that helps.
