My husband and I just came back from two weeks in Scotland and France. We flew to London on Virgin, taking us to LHR, and then connecting Luton to Inverness and Edinburgh to LGW on EasyJet, Stansted to Clermont-Ferrand in France on Ryanair, back to Stansted and bus to LHR. A nightmare to plan, including cancellations of flights, etc, and 8 different airports. However, it gave me lots of experience for this topic.

Bus service goes from all four London airports to all the others. BUT, allow more time than you can imagine. We planned on 1.5 hours from Stansted to LHR, and it came to 2.5 as the M25 was bumper to bumper almost the whole way. We barely made our flight.

EasyJet was no problem at all and it was our third time using them. Great prices, but be aware, as with Ryanair, that the price they quote does not include all taxes so that when you actually book, it is much higher.

Our Ryanair flight was 1.5 hours late leaving, but returning was fine. I had read on FT about their baggage surcharge, so we packed as lightly as we could. Going from STN to CFE, we were fine. Coming back, for some reason, they changed the weight requirements, and we had to pay an additional $62 for overweight luggage. And, they would only take a credit card. We had been having problems with our AA Mastercard since they didn't like us using the card for foreign travel and decided it was fraud, so they put a hold on it and Ryanair couldn't get it to work. Another story for another post. The point is, the excess charge and they would not take cash.

We actually had one of the best trips of our lives, even with all the juggling. Hope this helps.