TBH its more about personality than age. Mine are (will be) all between 2.5 - 3 years apart. My biggest struggle are the girl.
DD1 is jelouse of DD2. They are close in age, but a good distance apart so that DD1 doesn't (or refuses) to see why she is expected to do more to help than DD2.

Everything is competition with DD1 & she makes DD2's life very hard. She's better at so much, but she doesn't get that its simply because she's older. For some reason she needs to prove that she's better all the time.
DD2 & DS are completely different. I have them sharing a room & it will stay that way for a long time, because they get along. They have fun together. They do fight sometimes, but its nothing.

I think all you can do is do what you feel would be easiest for you. I wanted mine close enough together to grow up together, but far enough apart that one was out of day nappies before the next one came along. It kinda worked that way so far. This one has changed all those plans though, lol.

An older child can be a huge help though. A friend of mine has 2 DD's. DD1, almost 7 & DD2, 4 weeks. Her DD1 does alot coz its all so exciting. Gets nappies, clothes, towels etc. That little extra pair of hands can go a long way