0 to 1 was harder BY FAR for us.
1 to 2 hasn't been a big deal at all.
Part of this is that my second baby is muuuuch much easier personalitywise than my first. My older son had bad reflux until he was about 9 months old and also was just less laid back, slept less, etc. If I'd had them the other way around and had the easy baby first, then 1 to 2 might have been harder. :)
But I do also think that for me at least, a large part of going from 0 to 1 was having all these life changes I didn't even think about/couldn't have foreseen. I remember realizing, when my son was a couple of days old, wow: I will never not be responsible for someone else again in my life. Just wrapping my head around things like that was really hard for me.