Under a week to go & Need for recommendation

I introduced myself a bit over a year ago, but have been mostly in lurker state, and now that I'm less than a week from departure I thought I'd introduce myself again!  Next Monday I leave from Portland, Oregon arriving in London on Tuesday  

As for my question...if you had 5-6 hours to waste in the proximity of a London rail station, which one would you choose?    I'm flying into Heathrow around 10.00, but my friend who I am staying with doesn't get off work til around 17.30, so I have a nice chunk of time to occupy myself!  I have no problems doing this, but I'm just trying to decide where.  I plan to  take the underground from Heathrow (I realize the Heathrow Express would be faster, but heck, I have time to fill!) and store my bag at one of the luggage storages at one of the rail stations (King's Cross, Paddington, Charing Cross, etc).  I just don't know which one to choose :b  Any recommendations?

I'd leave my luggage at King's Cross and head over to the British Museum.  I could spend all day there! 

That's a good idea; when I was in London last year we only got to the British Museum shortly before closing and didn't see much.

And the British Library is in close proximity to Kings X, not sure what they have on at the moment but its free!

I'm a big fan of the British Museum, but if you are really tired there are some hop on hop off tour buses that go around London.  One picks up at the British Museum, and you can ride around getting a tour if you want to not do much, or you can get off at a stop and see something and get back on again.  I do this with my parents sometimes when they just get in to Britain, and are tired.  Plus there is the tourist cheese factor!   

http://www.theoriginaltour.com/

I introduced myself a bit over a year ago, but have been mostly in lurker state, and now that I'm less than a week from departure I thought I'd introduce myself again!  Next Monday I leave from Portland, Oregon arriving in London on Tuesday  

We're in Portland now and leaving next year for England- I'd love to hear your impressions and how you get on! What are you going there for?