for me personally, the age gap between my two is perfect. 3.4years apart, and they get on well DD is old enough to accept losing some attention and wants to be involved, understands more about what she can and cannot do and that mummy and daddy need to share our time and is happy with that, but not too old that she has grown used to our attention alone and resents it being split. Little things like not having to be carried across the road, or be old enough to expect her to hold on to the pushchair and not run off.
The jealousy is minimal and she absolutely loves teaching her brother how to do things -talking, walking, playing with toys, eating (or not), encouraging, it is also helping her development, in terms of compassion and empathy, but also her reading (she loves to read to him) and practising her own skills so she can help him better.
And I think the age gap is stll small enough that they can grow to be friends as adults too.
I know several people with two and a closer age gap, and they struggle with doing lots of things that require two people if only one adult is present, but then, their children are still under 3, and I also know people with much closer age gaps as older children who look after each other and are very close so it works for those families now.
And at the end of the day,you can't always chose the age gap can you?