Hi prat
It really depends what kind of flying you want to do, and how much you would be willing to earn for the work.
If you fancy doing a mixture of longhaul and shorthaul flying without waiting for about 2-3 years, and are not overly concerned about exactly how much money you will earn, then maybe Gatwick is for you.
I don't know exact average figures, but I've heard from ex-LGW EUF crew (now at EUF LHR), that take-home pay was about £1200-1300/month, but that you worked very hard for that money. This puts EUF LGW salary in line with virtually all other LGW-based (and other) UK airlines.
At Heathrow (EUF) you can expect to earn more than this, £1500 in an average month, or more if you request overtime or have a busy roster.
In answer to your question, YES EUF LHR is certainly worth it - better money, more nightstops and the opportunity to fly longhaul in the future (you need to put your name down on a list, but only when the list comes out; I'm not really sure how the system works).
At LHR, you start on shorthaul, but this is a very nice and relaxed style of flying!
Good luck