+1 on the EasyJet once you get over there, book long enough in advance and pay like $10 a seat, the unlimited-weight-as-long-as-you-can-carry-it-yourself has proven more than useful for me in the past.
Also, I've never flown through Frankfurt, though I've done Schiphol, Heathrow, Gatwick, Stanstead, Luton all often enough that I wouldn't bother. You're probably better off going to Frankfurt for any continent-based travel, then hop on a german ICE fast-train, book up to 90 days in advance and you can generally get anywhere between NL, Belgium, Germany, Denmark, Poland, Austria, Switzerland for as little as €30, much preferable to flying and take all you can carry (also, you get as much leg-room as business class on a plane).
Unfortunately the times are almost gone when you could easily get a 0.10, 1 or 10 Euro ticket (+ taxes) from the low fare airlines in Europe, rather calculate with 50 to 100 Euro for each flight now. If you choose a connection flight with one of these airlines check their luggage policy carefully, some charge a lot for each individual piece of lagguage or based on the actual weight. Avoid Ryanair, they have a horrible pricing system. You will have to pay to pay your ticket with a credit card, you even have to pay for check-in. Ryanair is thinking about replacing seats with some kind of stools and they even plan to charge you for using the on-board toilet.
Be aware, that some of the low fare airlines (e.g. Ryanair) call they destination London or Frankfurt or watever, but actually they use airports which are far outside the city centers which takes a lot additional time for transfer. Often these airports are not the main airports with the intercontinental connection flights, e.g. coach transfer London Stanstead (Ryanair) -> Heathrow will need up to 2 hours during rush hour.
In general, I would recommend to book your flights from a single carrier, than you are on the safe site with your luggage size and weight.
IMHO Heathrow is ok if it is your final destination or if you are using BA and a connecting flight also with BA. Then you do not need to change terminals (BA has a new one and the luggage problem from the opening time seems to be solved), but it might not be a very good idea if you take a different carrier to Heathrow.
Many do not like Schipol, I think it is fine. Normally the queues are short, but the food corner could profit from some extension.
Frankfurt has meanwhile finished most of the terminal reconstructions which was necessary because of the introduction of the A380 fleet to Lufthansa, I can not say anything bad about this airport. The railway station is convieniently located next to the terminal building.
If you are using Delta/Skyteam, Paris might be the first stop in Europe. It would be wise not to choose tight connecting times there, it usually takes a little bit longer there (long walking distances!).
But if you found a flight which looks good to you, just take it, enjoy and have fun!