For me personally, I find the A330 more comfortable on red-eyes. Single aisle on the 321LR in my experience has led to a lot more foot traffic, both passengers (from both J and Y) heading up to the J lavatory, but more so cabin service. Some might find this bothersome (e.g. noise, vibrations etc.), e.g.if you're looking to get some sleep shortly after take off, while service is still going on for the rows behind you.
A bit of an unsung hero for light sleepers imo is 2K on the A330 (not sure about 2K on 321LR). Extra footwell space, also far from the aisle activity. Last couple of times 2H was free so also direct aisle access.