Okay lets talk about Yayiko or Nagoto both of them had goal to make world a better place, both fail but they found successors which would try complete their goals, so kinda they die happily.
Yayiko die really happy, his death was for best friend.
Nagato same, he die for hidden leaf village and found successor.
And talk which one had worst childhood is difficult. Because you had to feel it, you cant just analyze it and say definitely this one had much sadder childhood.
Especially Nagato and Yayiko had good times too. With J-man, with early Akatsuki while they were fighting for good goal.
If you compare numbers of family members they saw deaths Sasuke > Nagato.
Compare situation where Nagato was with y-man and Sasuke was with kakashi team i would say equal.
Over all main different is how they complete their goals.
Sasuke's goals was fails. While Nagato had a good goal and even he fail it he found successor.
Sasuke chose not to have good times, he refused to try and move on with his life, and through doing so brought more suffering onto himself. You wanna know why people like me have less sympathy for him? Because, unlike all the other villains (outside of Madara) he refused to change until that was his only option. Gaara, Nagato, and even Obito all took the first chance they were given to change their ways, but Sasuke? Unlike the others he was given multiple chances, and every single time responded to the person lending a hand with a knife (or chidori) in the back. You Sasuke fans, you're always so biased, to the point of total irrationality and hypocrisy. You act as if Sasuke had it worse than anyone, suffered the worst pain imaginable, and undermine everyone else's suffering to do it. You wanna know what I'd say is worse than having your brother kill your family (while that sucked)? Having your parents killed before your very eyes in a war that devastated your country, and then being forced to kill your best friend and being crippled in the process. Being viewed as a monster by most, a weapon by your "family", having the one person that pretended to love you try to kill you, and having your own father make multiple attempts on your life. Having no family or friends and being hated by everyone for most of your life. Watching your mother die at a young age, then having your father kill himself before your very eyes, watching your friend being crushed to death by a boulder, and then having your other friend force you to kill her, having your master and his wife killed and having your pupil betray you, and, along with all of this, your friend turns out to be alive and evil. All of those characters, just about had it worse than Sasuke (Naruto, Kakashi, Nagato, and Gaara), and, Obito had it likely just as bad, possibly worse, considering that his life was the same as Naruto's, except the one person that cared about him for most of his life (Rin) was killed by his (only very recent) best friend before his very eyes (so, essentially, the same thing that drove Sasuke insane, to all you idiots that say the only reason he flipped was because a crush died). And then you're always hypocritical and point out how all of those characters are Shinobi and should just deal with it and that they should expect people to die, well, guess what, Sasuke was a Shinobi too, by your logic he should have expected his parents to die horribly no matter how and why it happened. You Sasuke fans are so annoying.