That depends on the fans and what you are trying to achieve. Post your computer specs and what you are using it for.
Also are you overclocking?
Cpu: i7-4790K
Motherboard: Asus Z97-A
Video Card: Gigabyte Geforce GTX 970
Case: NZXT Phantom 530
I listed the stuff that only matters. I'm going to be using it for gaming and well just trying to find out if having 2 200mm fans is better than 3 120mm. And yes I will be overclocking.
If you looking for High airflow the 120's are the way to go. If your looking fo r decent airflow an more quietness go with
200mm fans.
So is having high airflow good for exhaust fans?
Yes when you want to move air when you are gaming, and stressing your cpu and gpu. I use high airflow fans but I have them on a Fan Controller. When I am Gaming I turn them up all the way. When I am surfing the web and taking it easy I turn them down.