Mayfair Hotel

What do you mean by "good"? What is "good" to you? There are several stratospheric hotels in Mayfair - some of the top London hotels are there.

I mean a 4 or 5 * Hotel in a good neighborhood close to sites and tube.

Zahra, I just booked the 5* Intercontinental in Mayfair on Priceline for 3 nights at $160/night. That's $s, not GPs. Amazing Deal!
See betterbidding.com

On the edge of Mayfair is a Holiday Inn. We've stayed there a couple of times, there are sometimes deals. Its big advantage is that it is near Berkley Square, just about opposite the Ritz (another option) and across the street from Green Park Underground. Walking distance to Buck House, Piccadilly, Hyde Park. Easy walk up from Piccadilly Line Underground on the Piccadilly Line from Heathrow. I'm not sure if it is 3* or 4. Certainly the Ritz is 5 or 5*+.

Washington Mayfair Hotel. A very short walk to Piccadilly and Green park tube station, at Shepherds Market. Not on the main roads Very pleasant walking to Bond and Regent street and even up to Oxford Street Stayed there many times. ( 4 or 5 star) Also try hotels on Jermyn Street (one block south of Piccadilly, very elegant address)

The Lanesborough is a five star in that area.

I have stayed at The Park Lane a few times. Its one of the Starwood properties. It's a short stroll to two tube stations and the rooms are huge even by US standards.