haven't done A321NEO myself, but here is a couple of reviews on JFK-GYE with B6 https://airlinegeeks.com/2019/12/13/38493/ and https://thepointsguy.com/news/jetblue-airbus-a321neo/

Some useful comments in there about the best seats. They are using slim line seats on their flight just like.everyone else. It's not going to be as comfortable as their old leather seats, but I haven't read any reviews that said the new seats are that uncomfortable.