My experience flying both CFM and IAE powered A320:
- As said before, engine starts on the CFM are way faster
- Residual thrust is higher on the IAE either in ground or in flight idle. It just starts rolling when you relese the brakes and floats a bit more after retarding the thrust levers. Thrust control for taxi is also more linear and smoother on the IAE
- While its a bit easier to set the stabilization 50% N1 on the CFM than the 1.05 EPR on the IAE, in my experience, the IAEs generaly spool up nicely equal, while on the CFM powered ones, one engine seems to always hang quite a bid behind the other one at first spool up.
-Low down, the CFM feels a bit more powerful than the IAE, but up high, lets say above FL250, the IAE has noticeably more thrust reserve left beyond the cruise setting.
Personaly, my favorite is the Pratt on the NEO, lots of power and very silent!