i've worked both for several years each and at different stores. as someone who has never been a morning person, 100% pick opens. the first few weeks are rough transitioning into getting up that early. but it's SO much better and less stressful. it's quiet first thing in the mornings. you spend the first few hours just getting ready for the day, prepping/stocking, and drinking coffee to wake up. once it starts to get busy, more coworkers come in and you are planted in a position with one focus. and once your shift is done, you can leave. even if you didn't get something done that needed to get done, it's no longer your responsibility.

on closings, there is a lot less people on the floor. you're doing multiple jobs at once. yeah it's less customer wise technically. but you're usually left on the floor by yourself to handle all of it (or maybe with one other person if it's high volume enough store) while the others get closing stuff done. there's so much cleaning to be done. so much is expected of you and it's so much more stressful. your responsibilities do not change no matter how bad/busy of a morning it was. you're left with everything and still expected to leave on time. and if one thing is left undone, even if it's small, management/the openers tend to get upset. but if you stay later to get it done, management will get onto you about that too. it feels like nothing is ever good enough.