I have flown all three x- country (PHX - JFK or PHX to PHL or PHX to CTL) , I like the A321 best (CEO or NEO), like the overhead bins and feels more spacious overall. The 737s, not a fan of the pivot bins (but glad they are large) and the seating just feels more cramped (although I did measure and both none MCE seats were at 31 inches). The 737s windows are bigger and let in more light and allow for better views. Bathrooms are better on the A321s but overall both are similar experiences.

Note: the 737s have a smoother ride overall and the Max and NEO are significantly quieter but that's just technology evolving over time.