What is the best way to get to and from the London airports to the Southhampton cruise terminals?.
Train via London. Of course, additional information concerning which airport would have been helpful for a better answer.
1. Which airport? London has 6, and both Heathrow and Gatwick get nonstop flights from the US. 2. What do you mean by "best"? Fastest, cheapest, easiest, or something else? 3. How large is your group, and how many bags will you have? Etc. Help us help you. You should also look at www.cruisecritic.com. Here's their Forum that covers Southhampton: http://boards.cruisecritic.com/forumdisplay.php?f=233
Look on www.nationalrail.co.uk/ They have trains from London Paddington to Southampton about every half hour. You'll need to get a cab over to the ship from the Southampton train station.
You might want to find a map of the U.K. trains to see if there are trains available from your airport without going through London. Like was said, the info provided was a little short.
If it is Heathrow you mean by "London airport" there is a National Express bus that goes from the airport to S'hamptom. Go to nationalexpress.com for schedule, fares, etc. Once arrived in S'hampton it requires a taxi ride to the docks.
Southampton is served by trains from Waterloo station in London, not Paddington. If you are flying into Heathrow the best way would be to get the Railair bus to Woking to change to a train to Southampton, which avoids having to cross London. From Gatwick your best choice would be to get a train to either Victoria or Blackfriars stations in London, then take the Circle Line from either of those to Westminster and the Jubilee Line to Waterloo (or if you have lots of luggage for a cruise, take a taxi).