I just got back from a similar trip (only 3 days in country). I spread my visits to the Le Meridian Pyramids, Le Meridian Heliopolis and the Sheraton downtown. My favorite hotel by far was the Le Meridian Pyramids. As a plt they upgraded me to a two room suite with a great view of the Pyramids. They also gave me access to the club room that had food and free wireless internet access (which usually runs about $35/day in Egypt).

If I was to do my trip again, I'd spend two full days at the Pyramids walking around and taking it in. I had hired a guide recommended by TripAdvisor.com but was not impressed... I was rushed everywhere and the information was what I could have read out of a book. Plus there are guides everywhere at the sites so you can get one there if you want.

The Sheraton Downtown was nice as it was right on the Nile and was very close to the National Museum (which is a must see as well). The hotel was okay, I was treated very well as a Plt. as i was upgraded to a large suite in the renovated tower (although it was a smoking room) and was given free breakfast.

The least impressive property was the Le Meridian Heliopolis as it is close to nothing (but the airport) and about a $20/taxi ride to the Pyramids. Although they do offer a free shuttle to/from the airport.

Lastly, the locals mentioned that tourism is way down this year and so the guides, porters and people at the sites are much more aggressive to "get" your business or tips.