the difference in screen size is amazing. it doesn't seem like much, but the first time the numbers pop up to unlock, you'll be blown away.
the 3s are getting hard to upgrade, since they don't have enough memory, with people having to unpair just to update the OS,
I have a 5, wear it full time (even to sleep), I turn off AOD off from 11pm to 8am (using automations in the shortcuts app on my phone) I get about 36 hours out of it, meaning if I charge it one morning, I'm still good until the next evening. So I still have to charge daily, but it's a bit flexible if my schedule is strange. with AOD off, I might get 48 hours.