The Airbus A320 autothrust is reasonably ok for most normal ops where the wind is not too strong. However it is slow to respond to speed loss - just observe how it allows the speed to decay below target in an Open Descent.
Hang on, that's a completely different aspect of the autoflight system, since in open descent autothrust commands idle power and pitch controls airspeed.
I agree that the A320 can be a bit thick when it comes to speed control in open descent, particularly at higher altitudes with an increasing headwind. There's a tedious inevitability about the way the speed ticks towards MMO with no response from the aeroplane to pitch up and arrest it, yet when you do intervene manually it's a tiny input to sort it out.
My experience is that the autothrust on approach is very capable and I can only think of a couple of occasions where I've disconnected it on the grounds of not being happy about how it's managing the power.
Having said that, our fleet is entirely CFM. Having only flown an IAE equipped 320 once (and floated down the runway during the flare), I wonder if the engines have slightly more inertia when it comes to spooling up or down, which would give the impression of autothrust being slow.