I've recently done the 321neo in F in both window and aisle with an in-cabin pet. Window felt more cramped underseat, though still doable. On the neo I would still strongly prefer the aisle because it's hard enough getting out of that darn window seat without worrying about the pet at your feet.

(I always tell my seatmate, because, while my dog sleeps most of the time on the trip, when the plane comes to a stop he often lets out quite a screech to remind me that he exists and should not be left behind. Which, I hasten to add, has never happened!!!)