Well, I just wrote 60 lines in response to your request, and deleted it, realizing my main hope is that you not compare your children. A child can't be less cautious or clingy because her parents want her to be. A child can ultimately learn to deny her genuine emotions and needs if a parent insists on it, but she won't be a different person. The needs will just go underground and emerge in some other way, perhaps more troubling.
And if your kids weren't so available for comparison, I'm guessing you would have less trouble making allowances for each of them. It must surely be harder to do that when you have one who's relatively easy, and one who's relatively needy.
Discipline is a whole other area. I've known dozens of families with young children, and those who practice compassionate parenting with empathetic communication and clear expectations have always ended up with great kids. The early years are a challenge, no matter what techniques you employ, because there is a long, slow learning period in which children are often frustrated by their parents' requirements and schedules. Rather than "correcting" or punishing a child so young, what usually work are distraction, redirection, anticipating problem situations and avoiding them whenever possible. All good strategies.