This is always an interesting topic
ATM I think I can name my top 4 fairly comfortably and in order - Bradman, Sachin, Sobers, Hobbs
After that it's ****ing tough. My gut says Smith, Lara, Gavaskar and Headley in some order for positions 5 to 8.
Then I would like to include Hutton, Hammond, Barrington, Dravid, Ponting, Kallis, Viv and Chapple somehow as 9 to 16.
No idea at all who I'd include ATM to round out the 20. And I'm sure if I dig into it, I might find some names worth displacing those in 9-16.
Some interesting lists here.