My two were as different as night and day.
My son was a "spitter" until he was over a year old. His napping was unpredictable; a lot of the time I could not put him down; I had to sit holding him in my arms in the recliner so that he could sleep at all. When he got overtired, he'd get so wound up it seemed like he couldn't find "sleep mode." I said he at least gave me points for trying - he didn't just scream no matter what I did, but he varied between "fussy days" and "very fussy days." At least holding him helped - though it seemed like I did it so much, it amazes me that he learned to crawl at all. It got a little better when he started walking (at 8 months), but then of course, I had to keep an eye on him. He either had to be hanging onto me, involved in whatever I was doing, or heading off in another direction, in which case I had to follow him, because he simply didn't come when I called him. I felt like the world's most clueless mom.
BB2K was totally different. In almost all of the pictures we have of her as a baby, she is smiling. She pretty much only cried when she wanted something, and I was amazed to realize that I usually knew what she needed before she did more than whimper a bit. Glory be, the child could sleep on her own, and even play contentedly nearby while I got other things done. Oh, yes, she had fussy days too, but even at her worst she never got near what her brother did. A lot of the time, she got along fairly well with her brother (one of my favorite memories is of the two of them "cooking" with some old pots while I was making dinner), but I had to stay close because I knew the peace could be short-lived. Like his father as a child, he had a nasty temper, and since he is 4 1/2 years older, I had good reason to fear that he might seriously injure her when he blew up. Thank the Lord, he outgrew that, and they became the best of friends.