I'm biased but i will give you my thoughts.
As you say the 320 has the cleaner dial, both have GMT but do you need that function? The third hand can at least be hidden behind the hour hand which is a nice feature. Both have a 'seconds reset' function, which is also nice and there is a PR display on the 320 too, though of a different type to the 321 and on the back.
I think the 321 and the 90 before it with the off-set PR indicator, which is pretty pointless on any auto frankly is just butt ugly.
Well, i did say i was biased
