The Hilton near Term 4 at Heathrow is a nice, albeit spendy, place to stay. The rooms are very European, with smallish baths and tubs that require a high step up. The beds are comfy. The food is reasonable but pricey. The only thing is that there isn't a whole lot to do around the hotel. It is, however, a pretty easy ride on the Picadilly line to major stations: Kensington, Piccadilly Circus, Covent Garden, Kings Cross, etc.
About an hour and 15 minutes from the hotel, starting with a 5 minute walk under a covered walkway to Terminal 4 for bus connection to a nearby station (Hatton Cross, I think) to connect to Piccadilly line. I bought a day pass for 6.30 pounds, and took a train ride to Covent Garden. Covent Garden is a great place to launch in London. It is deep undergound, so don't think about the stairs, wait for the lift. It is at London's West End with all the theatres, and was once a public market but now a slew of artsy shops (and at least 2-3 Starbucks). A pretty reasonable walk from there to Trafalgar Square, Buckingham Palace and the Parliament Bldg where the Clock Tower holds Big Ben (the bell, not the clock).
I like this hotel for overnight business connections as you can get into Heathrow without the Hotel Hoppa or a 15 pound cab ride.
- Free Wifi