Personally, Amber is one of the best restaurants I have ever eaten in. Since the early 1980s, I have been going there and the preparations are just the same. the mughlai food is excellent.
My personal favourites which I would recommend to non-vegetarians are mutton moti biriyani, chicken bharta and prawn butter masala. The taste and aroma are just divine. The taste is distinctive and nowhere else does it taste the same. Those who go to calcuttta, should definitely visit Amber.
In the 1980s, Sagar, which is run by the other brother( so I have been told) was very good. But over the years, the ambience of Sagar has deteriorated - havent been there fro a couple of years, so dont know the exact status now. Earlier, both these restaurants were identical in class and quality.
The only problem is parking, you will have to park the car some distance away - the palce is usually jam packed. Also, I wouldnt recommend going on weekends, especially in the evenings as there might be a huge queue of people waiting to get in!