What do you say performs better?? Trying to get an upgrade for my rig but not sure which one would cool it better... Any thoughts?
Other things being reasonably equal, you'll always move more air through a 140mm fan. The A12x25 is a lovely bit of technology, but it can't match the airflow through the NF-A14.
If you were constrained to a 120mm fan then I would pick an A12x25 over pretty much any other fan, ignoring price.
If your case will fit them, 140mm are generally more efficient than 120mm fans. When it comes to static pressure for radiators, however, smaller fans are generally better at pushing air through radiator fins, but most good quality fans between 120 and 140mm should be fine. It's only when you get to sizes like 200mm where it's really obvious that larger fans struggle to push air through those fin stacks.
If your case has room for something like two 140mm fans or three 120mm fans, if you really need the air flow, I would always go for three 120mm fans. While the 140mm fans would be more efficient, a third fan would tip the favor back to the 120mm fans as you could run them at slower speeds (for quieter operation) and achieve the same thermals.