Full size or mini diaper bag

Full size always!

Bigger is not always better. I had some big ones and they were over kill. If you can afford it the petunia pickle bottom boxy backpacks with the front fold out changing pad is like the perfect size. I had one with my daughter and going to do it again for this baby. It's big enough to hold everything without feeling like a suitcase

https://petunia.com/collections/backpacks/products/boxy-backpack-in-brioche This style of theirs. I love it.

Full size if you are traveling to see family for the day. I always needed extra clothes because the baby spit up and throw in 2-3 of the baby’s favorite toys. Daycare I only gave a lunch box cooler everyday. Daycare center had us drop off spare outfits and sleeves of diapers the first day, and replenish gradually as needed.

Definitely full size just being ready for the unexpected is best for me

Bigger is better and I have ALWAYS LOVED my backpack diaper bags keeps me more hands free for baby's needs

I had a big one that was useful at the very beginning with how much you might need with a newborn, but then I switched to one I was given with my breast pump that was insulated at the bottom and that was a lifesaver! He’s a toddler now but I still use it everyday to carry snacks, drinks, etc.