I can't comment on EasyJet, but I can say that I was really pleased with Ryanair when flying to and from London Stansted to various Scandinavian destinations. The seats are more comfortable than for Air Canada flights of similar length. The staff was fine.

I read that Ryanair has the same aircraft servicing contractor that Lufthansa does. I'm not sure what EasyJet has - but if it will make you feel better, you could look into that.

If you need to return to London for a return flight, I would add plenty of time, probably at least an overnight, for peace of mind (that's what I did). Also consider the worst case scenario and how to deal with it. But Ryanair has an excellent record for on-time arrivals and departures.

There are buses that transport you directly between the major London airports - still you have to allow oodles of time for all the delays that can occur.