I miss my siblings, so I like them.
I have three of them. My oldest is five years older, my next oldest about three and a half years older. My sisters were very mischievous with me when I was young. K would usually lead the teasing, while D would be both quieter and more sinister, teaching little speech-impediment me to say "I was born on a pirate ship" (I was so proud). We got along though, pals on car trips, compatriots when we screwed up and got lectured, and frequent playmates. They grew up, and I did soon after - we don't keep in as good contact as we should, but we get along well. K is boisterous and a little quirky, D is civil with a snappish wit, and I'm the slightly quiet, goofy upstart. The best part is that we're all more than that.
Then there's my younger brother. I list him separately because he's so far out from us in age - 9 years - that there's a significant part of my life where he was not. My sisters and I were supposed to be it, and we had our own, long-ingrained dynamic when we learned that our mom was pregnant. I went from youngest to middle, from center of attention to left-of-camera. I resented it a little. I pestered him some. Even at the time, I wondered why I did it. I liked him - hell, I loved him - but as a 13 year old I'd do stupid things like lifting him up and setting him into an empty trash can at the ball park. (He started crying and I got him out.) I got to see him through the first half of elementary school, just S and I home most afternoons after I got him from the bus stop. We'd hang out, play games together. When I went to college, I missed most of the rest of his childhood. (He's a year from college now.) He's grown from being a tormented extrovert only in tenuous control of his temper into a cool, relaxed young man. I view him as friend and brother, and also a little like a nephew, someone who does sometimes need a little advice in the form of a lecture.
My partner calls our sibling dynamic very competitive. Perhaps it is, but we don't (any longer) bite each other's heads off when we lose a game.
I expect that siblings are the sort of thing that I never needed. I could've been happy without them. However, having them was an experience that I wouldn't want to miss.