I know comfort is a very subjective thing but my flights on the ATR have been far more comfortable than those on the Dash 8. I've flown on the Fokker 50 but too many years ago to be able to remember how it compared.
In the Aer Arann fleet, there's quite a difference between the 20 year old ATR-42s and the much newer ATR-72s.
Never been on a Saab 2000, but I have been on the similar looking BAe ATP.