I've flown EasyJet and RyanAir. They're fine. RyanAir tends to have routes at out-of-the-way airports more than EasyJet. In the case of Rome, however, they both fly out of the same airport-- so make sure you check RyanAir
, they probably have a cheaper fare than EasyJet for the day you want to leave!
Beware that you will be flying into London's Luton or Stansted airports and you'll need to get into the city from there, and you can't take the Tube. From Stansted you can take the Stansted Express train
, but it's pretty expensive. I recommend booking a seat on a coach instead, there are TONS of them all day long going to the city center and you may score one of the special internet rates of 1 pound. (It's not expensive even if you don't get that rate.)
Check out National Express.