<p>Pizzagirl, I don’t think there is a big time differential between one way or another on average. On any given day, the tube might be quicker than the cab; or a different day, it might be the other way around.</p>
<p>The one thing I would suggest (in fact, suggest strongly) if you decide to tube it: Go online and double check that all the lines you need are operating. If they take a line out for maintenance, they usually do it on a Sunday. I think that at least one line has been out of service every time I have visited. If any one of your lines is out of service the day you arrive, you should definitely take a cab. Have fun!!</p>
<p>If you are arriving on a Sunday and the lines are all operating (as hayden said, there are frequently works on the weekends) then the tube would not be a bad bet. Holborn is on the same line as Heathrow so you do not have to change trains. And on a Sunday it should not be too crowded. It should run you about 4 pounds each to get from Heathrow to London on the tube (unless it has gone up since last year). </p>
<p>I am arriving on a Sunday also in about 11 days. Hopefully the Iceland Volcano will not cause any disruptions to flights.</p>
<p>When we went to London last year our hotel arranged for a private car service to Knightsbridge. It was a bit more expensive (because we were four as well) than a shuttle service. But it was far less hassle than the tube. One of my daughter’s friends was on the same flight (I didn’t offer her a ride because I didn’t want to be the proverbial Jewish mother and embarrass my daughter with hovering.) and she took the tube. It was a nightmare and somehow lost all her initial spending money. (Not a lot, but dinner cost was a problem.)</p>
<p>After a long plane flight I want someone there with my name on a placard, a hotel to go to, and a cup of coffee or tea at the hotel.</p>