Recently I began using FlatPress on a private directory on my web host's server for documenting my work notes. (Previously, I just did it with word processing software on my work desktop, but a new job has me working in multiple locations). Thus far, I've been happy with FlatPress.
I avoided the "normal" online note taking sites because I wasn't thrilled with the idea of putting my stuff in a space where I wasn't sure how much control I'd have. In part, this was because one recommendation I found on the web as "the best" had a one page site that said, essentially "Going out of business, get your data now or lose it!" (I know the owner of my web host personally, so have no fear that they are going to go out of business without my knowledge, or that they'll misuse my data.)
FlatPress is a blog engine, but it uses plain text files instead of an SQL database to store its entries. Thus back ups could be as simple as copying the contents of the appropriate sub-directory (fp-contents, assuming a default install).
If you are running a web server with PHP, FlatPress should be very easy to install: just download, copy into the directory where you want your blog/notes, decompress, and then navigate to that directory with your web browser and click on install/setup (I don't remember the exact term they use). I did this on a home PC running Windows with XAMPP before setting it up on the web server. If you're on Linux, you'll also have to make the contents directory writable before you do the install via the web.