I would suggest avoiding the Renaissance, although it has the best runway views of any of the airport hotels (as long as you're not facing Bath Road, obviously), but is tired, tatty, run down, and old fashioned. In its favour, it has good rates, I think I paid about £60 last year. In fact 'Renaissance' is precisely what it needs.
Most of the reviews on sites such as Trip Advisor will bear this out :
Renaissance Hotel London Heathrow Reviews and Photos, Hounslow, United Kingdom - TripAdvisor