https://standardnotes.com syncs well. cant speak to importing. they have an interesting privacy/encryption approach and some (all?) open source https://github.com/standardnotes
My bigger gripes are that it doesn't support (markdown) formatting without a subscription, and I can't figure out how to put notes into folders.
I only use the free version of Standard Notes, but I am a big fan of the product. Their syncing has been the most solid/problem-free I've seen amongst all of the notes apps I've tried over the years.
Their selling feature (to me) is the privacy focus, because end to end encryption is the default, and a very rare one among other note apps I've taken a look at.
Sync works well, and is one way I use the app, even when I have other things like org-mode in play on some devices. It is typically quite handy to just paste something on my Linux desktop, and copy-paste on my iPhone to send somewhere iOS-specific.