I think everyones experience will be so different for a variety or reasons.
I may as well been a only child my brother ( whom I have not spoke to in15yrs) is 12 years older then me so we never had a relationship to start.
I wish I had siblings close in my age

. I grew up fine without them don't get me wrong.
I married into a family that is large my dh has 10 siblings! we have 4 kids so the large family we have was because I didn't like growing up basiclly alone and well he had a large family ;so it kinda continued. We are done with having 4 kids though

.
My dd has 2 friends who are only children- 1 is a spoiled rotten brat, dd does not go to her house or hang with her much because of how she acts. She doesn't share , throws tantrums and has to hang on her mom every chance she gets. the mom and dad buy her EVERYTHING she wants. Not to be mean but the gilr is 8 and acts like she is 3 or 4 yrs old
The other girls is the opposite she shares, she is shy , plays sports and does things kids do with siblings . you would not guess only child if you saw her and her personality.
I would not have a large family if you can not afford it, kids are expensive

. I think I like knowing they always have each other to turn to god forbid something happen to either one of us, and it helps them learn to get along with diffrent people. I have one dd 7 who is very sensitive and takes everything serious

, and my son 10 is very strong minded we but heads alot him and I

, my 4 y/o seems to be more of a practicle joker and smarty pants at this point

. the baby well she is to young yet to know right now she is a

. who knows what way she will go.
I think if you raise your kids to share and respect others and give consequences for bad behavior reward good behavior you should be fine with one child. Expose your kids to ther kids with sports, daycamps, clubs that helps a lot.