1-2 was by far the hardest for us. ODD, our first, was an incredibly easy baby. She napped like a champ, two good solid long nap blocks per day until she was about a year and then down to one good long afternoon nap. She slept well at night and was just generally easygoing and fun.
Then DS came along. He is a sweetheart of a guy but he's very sensitive and for the first year-18 months of his life, wanted to be on me 24-7. He nursed like a remora for the first six months (which was all new to me since ODD was adopted and not BFed), and barely would allow anyone else to hold him, including his daddy, until he was over a year. We'd be at birthday parties for ODD, who was only 2 when he was born, and the other moms of 2 would be able to hand the baby to another mom for a few minutes while they tended to their older child. Not me. DS would flip right the hell out--not just during the classic separation anxiety ages, but all the time. It was sweet how much he adored me, but also exhausting. Plus, he was a catnapper.
Plus, ODD's age at the time, barely 2, made it rough. She was old enough to really want me to play with her all the time, and to be getting a lot more stubborn and challenging than she had been as a baby, but not old enough to entertain herself for much of any time at all while I was tending to the baby.
So that first year was hard as hell. There were many, many moments during that year that I am not proud of.
On the other hand, going from 2-3 was relatively easy. It's still exhausting, of course, because as my DH says, we've gone from a man-to-man to a zone defense. If one of us has just one kid, the other has to have two--unless somebody's giving the other a big ol' break and taking all 3 at a time. Pickup and dropoff from nursery school/day care is like a highly choreographed but extremely messy ballet.
But ODD was old enough when YDD was born (almost 4.5) to genuinely help, not just be given make-busy tasks. She and DS are also great buddies, and so they could (and can) play together a lot while I'm tending the baby. Now that the older two are 5 and 3 (baby is 9 months), they're just generally a bit more independent. Both are fully potty trained (daytime, anyway), and they can do many things for themselves, so I can send ODD off to get dressed and just help DS with buttons; they can help themselves to snacks that we keep accessible for them; that sort of thing. It also helps that YDD is a super-sunshine baby, rarely cries and goes to everyone (although she is a catnapper just like her big brother). Watching the three of them play together just makes me all gooey inside.