Hi Jackie,
If I fly from heathrow i often stay over the night before, sometimes hotel or hotel/park deals. I tend to go for the "undercover hotel" on the holiday extras website. You dont know which hotel you are getting until you book although sometimes you can work it out from information given, once they named the restasurant so google helped, another time they named which hoppa bus stopped there, tells you breakfast time all helps in guessing which hotel but does it matter if you go for a 4 star.
What you do know is the star rating (choose 3 or 4 star) and you get it with massive discounts. By going this route last 4 trips I've had the renaisance, Arora, Park inn & Radisson.
Another tip is use the service buses to get to your terminal or hotel they are free in a zone around heathrow and often more regular than the hoppas which i think are expensive.
http://www.tfl.gov.uk/tfl/gettingaround/maps/buses/pdf/heathrowterminals123-13970.pdf
Not shown on here as it doesn't go to the central bus station but a 423 bus goes along bath road past most of the hotels and to terminal 5 (and back), again free.
To be honest i try get the hotels along bath road because they are on bus routes.
Mick