Pro Max is just bigger, offers nothing new except for the size and battery, and doesn't make sense to buy just because of it.
13 and 14 are very similar, not much difference, but if you want to future proof you can go for 14 Pro if you can get it with resellers or retailers.
I always prefer new phones, but there are people who opt for 2nd hand but that's completely your choice if you're comfortable with the risks associated (if any)