I found a 2 year gap easy. I was fully in parenting mode and became a sahm (gave up pre kids job to childmind two 1 year olds 5 days per week along with dc1 when Dc1 was 9 months, then had to shut down my childminding business in order to move a long distance away when I was 8 months pregnant, and became a sahm).
I had dc3 when dc1 and 2 were infant and junior school age and it was much, much harder.
With a 2 year gap it's easy to find your own routine and do things suited to both children. When you have a newborn and a 2 year old you can have a late start if the baby's kept you up all night (I don't mean get up late because 2 year olds don't lie in, but you can all stay in pyjamas and watch cbeebies and have a toast and milk picnic and doze a bit til 9am).
It's so easy to parent well when they're close in age, with activities and outings that suit both as soon as the baby's a young toddler (obviously before that the baby doesn't really care what activities are going on as long as he or she is close to a parent, warm, clean and fed).
With young school children you're in someone else's schedule with school, kids have activities and friends over/ agreement to be at set places at set times. So often I had to take the newborn off the breast before he'd really totally finished because we'd be late otherwise, or pick him up out of bed for the school run just when he'd finally fallen into a deep sleep after being restless and waking constantly all night. I was constantly catching up with myself, everything was scrappy and unsatisfactory.
Dc1 and 2 with a small gap were very close until dc1 was about 9, but that's personality I think. Dc3 with a bigger 3.5/ 5.5 gap was a cute toy or pet to them - they adored and spoiled him but he wasn't a peer or equal playmate. This changed naturally over time though and dc3 and 2 played together on a more equal level once they were about 5 and 8.5 - it took much, much longer than with a smaller gap for them to be playmates, though partly because dc2 already had dc1...
It evens out in the end but for the newborn and preschool years I found a 2 year gap much, much, much easier than older sibling/s young school age when newborn arrived.