It can be argued that Nourse didn't have the support that Pollock had. Nourse's double century against Australia facing O'Reilly and Grimmett and the century against England before war against Verity prove he's one of the greatest players of spin. After war he scored centuries against England facing Bedser and against Australia facing Lindwall, Miller and Johnston. His marathon double century against England gave South Africa win and a knock to remember.
I really can't split between Nourse and Pollock but maybe that some videos/footage of Pollock's batting got stuck in my mind, I'm inclined to put Pollock slightly ahead but it's arguable.
Here's a feature on Dudley Nourse by Stuart Wark: http://www.cricketweb.net/blog/features/93.php