We're trying to decide the best way to get from London to Dublin. Just heard about Sail/Rail. Any recommendations?
The "best" way would be to fly.
Agree, "best" way is to fly. The time you save can be time spent exploring either city. Fly.
You might wish to take a look at what I say about some of the places en-route in another post - should you decide to take the train from London (Euston) to Holyhead for the Dublin ferry.
https://community.ricksteves.com/travel-forum/england/itinerary-advice-for-london-to-dublin-to-include-liverpool-a-pretty-beach-and-garden
www.skyscanner.net will show you the flights. (Beware of baggage in hold charges).
The Sail/Rail discounted combo ticket can bring train/ferry fares down to be competitive with airlines, but are not necessarily cheaper and the trip still takes 7 - 8 hours.