The A520 is fairly narrow and does not impact cornering clearance like the wider M324 but the 324 can be a more comfortable pedal due to it's wider platform.
Much of the comfort stems from the shoes you use... mtb and touring shoes tend to be a little more flexible and walk-able so a wider platform can increase support and comfort while road shoes tend to be stiffer and a narrower pedal is often quite comfortable.
I really like the 324... value is good and the pedal is very smooth and solid as Shimano pedals tend to be.