I use plain .txt files stored on Dropbox as a cross-platform note system.I work on a variety of different platforms and so I've discovered apps for each platform that interact with the same set of .txt files:
Why not notes? I use it a lot and can do sync between mac notes/iphone/ipad. I used to enable gmail notes in the account settings so whatever I note I see them synced on all my devices. But also u can use icloud just I use more my gmail account..