Ha, ha, people are all different, children are all different. I possibly found the 6 months stage the easiest of the lot.
First months were, I think, the hardest because my firstborn was failure to thrive and just getting her to eat at all was a nightmare.
With the weaning, I didn't cook extra meals most of the time: I just mashed a potato or some veg that we were having anyway. We had those brilliant plastic bibs that catch the food as it falls. Don't particularly remember the mess at this age, though I'm sure I was nowhere near as skilled as my brother who managed to feed dd boeuf bourgignon at her christening without getting any of it on her frilly white dress. Those were heights to which I could not aspire.
Terrible twos I was kind of prepared for, like you take a deep breath before climbing a mountain.
Whining threenagers I found harder - my patience with whining is very limited- but thankfully they were also very entertaining in between, so I gritted my teeth and got through.
Preteens, yes our youngest was very glum, but we kind of got into the habit of ignoring him.
Teenagers- both of ours were actually very reasonable, pleasant people, but our eldest had both physical and mental health problems which took a toll on the whole family. If I could have had them without that horrible fear hanging over the family that might have been our happiest times.
It's all individual.