I would add Workflowy to that list. I’ve used it for years. It’s simple, intuitive, and easy to use. You can also share lists, even when you move them around.
The ability to keep everything in a bullet list that is infinitely nesting and zoomable is key in helping organize things. The apps for iOS and Android are also outstanding.
Simplenote (as you rightly note) is also great because it is the bridge between apps like nvAlt and Windows-based programs like ResophNotes. Its sync is flawless.