My kids are seven years apart, almost to the day, and the older one didn't have any trouble with jealousy when the younger one was born. I don't know if it's her specific personality, or if that's enough years that it was easier.
I think there are positives and negatives to either choice. I'm only 14 months apart from one of my siblings, and we fought tons when kids, but we get along well now. And we did always have another kid our own age to play with, although my kids enjoy playing with each other despite the age difference. My older one is at an age where playing with little kids is fun. But it is a different style of play.
One good thing is that the older was not interested in co-sleeping anymore even occasionally at 7, so I had an easy time co-sleeping with the baby, but OTOH I know a lot of kids still like to co-sleep at 7.
And it would be great to be done with diapers early, but then again it's easier to be diapering just one than two. And the older one is old enough to take the little one to the potty with her if we're out and it's inconvenient to drop everything to go to the potty.
They don't fight over toys because they are interested in completely different toys at their ages.