My iPad is my most favorite Apple product. Apple watch is second. iPhone and Mac are necessary, but I wish they weren't.
iPad is the most comfortable device for me for reading, and reading is what I do most during my waking hours. It's also decent for watching videos, and I find that I don't mind composing first drafts of stuff on my iPad, but editing, especially if it involves moving paragraphs around, is easier done on a Mac. I also need the Mac to manage my media files.
The watch I use for tracking my activity and sleep, and has been very good for keeping me motivated to stay minimally active.
The iPhone I need for when I go out, and it's pretty good for reading ebooks and saved articles in Instapaper, and I also use the camera a lot. But I hate using web browser on it and I wouldn't attempt writing anything extensive on it.
The Mac is the device I wish I didn't need but there are some things, some of which I mentioned above, that just can't be done on an iPad or iPhone.
Overall, I'm happy with my Apple products and not tempted to go back to Windows or switch to Android or other smartwatches/fitness trackers.