My daughter went through nb, 1 & 2 hella fast and has been in 3s for the longest. 3&4 are best to have the most of

Honestly as long as you don't open them you can buy whatever size and exchange them. My 17 month old is still in size 3 and my son was just barely in 4's when he potty trained at almost 3. So I'd say 2's and 3's but as long as you don't open them you can exchange them because you may also find you don't like one brand vs another

2-3 lol even 4. My baby has been on 4 since he was 7-8 months. He's tuning 1 next week

I stocked up on size 1 and 2.