The answer to this question is rather tough. As one can't rate beauty on a scale. Different people will have different perspective.
Still I will try and answer this based on general perception. When it comes to old actress Madhubala is the most beautiful. Counting among yesteryear actresses Waheeda Rehman, Meena Kumari, Hema Malini, and Sharmila Tagore were attractive.
From the 90s, I can think of Sridevi and Madhuri Dixit. Meenakshi Sheshadri was charming.
Among the recent years Aishwarya Rai, Katrina Kaif, Anushka Sharma, and Deepika Padukone are the most beautiful ones in my opinion.