As far as I know there are no hotels attached to terminal 3, but there is a free rail shuttle between 1,2,3 and 4 and 5 whichever you prefer. Terminal 4has a Hilton attached to it and terminal 5 has a Sofitel attached to it.
Hilton hotels have a 50% off sale at the moment for any stays at weekends inc. breakfast for until end of August stays which is a bargain.
Most other Heathrow hotels are serviced by the Hoppa airport bus system so it is easy to get to airport from any nearby airport hotels.
Have a look on tripadvisor for specific to named hotels for reviews, but even the best hotels cannot please everyone all of the time.
