I couldn't choose a stage, I had parts I enjoyed and didn't enjoy at all ages to be honest.
I love the baby stage when they are so totally reliant on you, loved breastfeeding and the way their little hand would rest on your chest and they'd stare up at you, didn't like the lack of sleep.
Loved the toddler years because they were so funny, didn't like the mess or the tantrums that come a bit later.
Liked when they were little kids for the inquisitive nature and teaching them things, didn't like them being so strong willed when trying to get them to do things they didn't want to do.
Teens, I liked the chats we had and watching them grow in to an independent person, didn't like the worry it caused some times or seeing them have friendship/relationship/school struggles.
My eldest is an adult now and I'm enjoying watching her become an independent, hard working woman who is in a lovely relationship and has become really caring and considerate to us. I'm looking forward to seeing her graduating uni, getting a job, travelling, maybe get married and have children.
There is always things to enjoy and look forward to at every stage.