My first 4 that I raised are all 2 years apart. It was the literal 7th circle of hell for so many years. I wish we would have waited longer between them. It was not fun for many years.
My oldest is 9, my middle is 6 and my youngest will be 3 in March. They each have about 3 years between them. I personally love the age gaps between them. They were each fairly independent and fully potty trained before I had the next, which made things way easier for me. They all have great relationships with each other and get along really well. My oldest and youngest are almost 7 years apart and still love to play together and spend time together.
My two sisters and I are all 3 years apart. (I was born, three years later my sister was born, three years later my other sister was born. I am the oldest and my youngest sister is 6 years younger than me.)
When we were growing up, the younger two were closest to each other (which was fine especially as I got older and into middle school and high school). Now that we are adults, my youngest sister is my best friend and we are the closest.
My older sister was born, then 4 years later I was born, then 5 years later my little brother was born, then 6 years later my little sister was born. My oldest and youngest sister get along just fine even though there’s a 15 year difference. I think the two younger than me were closest though