Yeah ubiquity of Keep makes it very sticky. Getting iCloud notes on a PC is a real pain and requires you have your phone most times (Apple browser logins seem to have much shorter persistence)
I use iA writer a lot, but would be happy with any iOS text editor, as I like keeping notes in plain text, and then iCloud Drive does my sync natively. On Mac I use TextEdit or vim.
That's why I use Google Keep --- which is pretty terrible... except it's free, it's everywhere there's a browser, there's an app for it on every phone/tablet, and it works offline when I sometimes don't have internet connection.
Works ok since I write notes in plain text, with some markdown notation (but without actual Markdown support in Keep).
In the past, I've used Notational Velocity and other fancy things, but I find plain text is best. And now I need sync on all devices, so went with Keep.