I think the consensus among my friends is 0-1 was the hardest (but most of them only have 2). For me, I don't think any of the transitions were harder than the other. They all required different changes; new challenges (like how to go grocery shopping with 3 little ones), balanced with things I had done many times (like changing a squirmy newborn in the dark at 3am).
Oh this is so awesome to hear! We just found out we are expecting #3 (totally a surprise, I was on the pill) and our kiddos are 28 months and 11 months. This baby is due on my oldest's 3rd birthday so we could very well have 3u3 for a bit. I'm glad to hear positive things about going from 2-3!
Re: Question for those who have 3u3 or +
0-1 was hardest, then 1-2. 2-3 was cake.