Add me to the list of people who have tried most of the offerings out there.

1. Notes and writing - I have used Evernote and OneNote for notebooks/research clippings before, and ended up with a huge database glut with Evernote (yes, I had over 20,000 notes, and you can't decide which notepads to sync) and a closed system for OneNote (you cannot export anything from OneNote, you cannot even switch from OneNote Business to Personal). I refuse to have all of my notes stuck in a database now. I want them in my file system. So they are in folders/subfolders in my Dropbox in the most accessible format possible (pdf, docx, or text). For my novel writing, I use text files in markdown format, accessed through the Notebooks App. It allows me to draft, do basic formatting, spell check, etc. chapters in individual files so I can jump quickly between them on iOS as well as Mac devices, and then I can compile them into one long docx or odt app when ready to send the ms to my editor and thence to Vellum.

2. Calendar - I'm with you on Fantastical! And the developer is responsive to suggestions/bug fixes.

3. Task/project management - Todoist - works on all of my devices, including adding items to my grocery list via Alexa. I can set up as many roles/projects/subprojects as I like, I can set up templates of projects and checklists to be imported (for each book I write, for example, I have a project template of nearly 100 tasks), and it never fails to sync.

4. For email, I use gmail. No desktop app. On the iOS devices, I use the built-in mail app. On the Mac, I find that nothing beats the gmail web interface, and I have a few Chrome plugins that enhance my use.

5. Apple Notes - Why use a notes app when I just said I won't use a dedicated notes database? This is just an inbox for notes for me. Syncs across all of my devices, easy to ask Siri to add a note when I am on the move, to handwrite a journal entry on the iPad (turn on, tap the screen with the pencil), or to send a page or text selection via the share sheet. I generally don't keep notes in Apple Notes for more than a few days. I move them into my file system (handwriting files print to pdf, typed files copy and paste to docx).