I'm planning a trip for next year (when hopefully all volcanic ash will be a thought of the past) to London and Rome. I plan to spend about a week in each place, but I'm not sure of the best way to get there. (I've only traveled in France, before.) Ryanair seems to be the cheap way to go, but are there any pros for taking rail?
For such a long trip, unless you're planning on stopping along the way, I'd fly.
Ryanair is fine. I've done London to Trieste, and Rome to Dublin, and we were fine. Just make sure you pay attention to their luggage rules, and check-in rules. They can change, are very strict, and can cost you a lot of money if you don't follow them.
That being said - flown them 2 times, great experiences all 3 times.
Check out Airberlin, mainly because they fly from Stansfield to FCO.