In your Opinion who is

The best actress
The most acttractive actress
Your favorite

You can have the same for the three categories but each one of them is a different thing.

Your favorite actress
The actress you enjoy watching the most for many very personal reasons

Your best actress is the actress you think is the most belivable in the roles they play and are very good at showing all the emotions their characters require.

The Most attractive is the combination of the best looking with great sex appeal.

Here my answers

My best actress is Glenn Close

My favorite actress is Catherine Zeta Jones

The Most attractive is Monica Bellucci