Last time I stayed at the Renaissance was about 10 years ago. It was very pleasant as I recall. My current hotel of choice when overnighting at Heathrow is the Doubletree on Bath Road.
There are a bunch of hotels around LHR, all accessible via the Hotel Hoppa bus service run by National Express. GBP 4.50 each way if you pay on board, or GBP 4.00 bought in advance.