WebDAV: not crazy about exposing WebDAV to the outside world
Filesystem: nope, looking for a remote mirror that works w/ mobile devices
Nextcloud: not crazy about hosting it myself
Dropbox: maybe
S3: maybe
Looks like Dropbox is the best choice as S3 is in beta.
Anything to be aware of w/ Dropbox or is it a seamless integration?
Self-hosted Nextcloud is generally the best option because it's faster and without restrictions. Dropbox works well in general but I think they throttle connections when you sync a lot of data, which might be annoying when you setup a new device. If you don't want to self-host though, it's probably the best option.
I am using nextcloud, works fine, but please understand nextcloud is using webdav too. Here is another solution, which I tried, with limited space (2Gb or 4), but otherwise perfectly fine and free.
and has been around for some 20 years without ever forcing customers to buy plans or restrictions.
I tested this a few days ago, admittedly with a small test DB and from Android. Carefree !
You can use filesystem and use another cloud service like syncthing, resilio or mega.
As for nextcloud there are plenty of servers so you don't have to host it yourself like opendesktop
My requirements are pretty simple, so I've been using Dropbox simply because I already had the account. Would you please describe why you prefer pCloud? I know nothing about it, but if I understood its advantages, perhaps I'd switch.
In general I like pCloud over Dropbox because they have a lifetime plan. I'd rather pay once than get stuck paying over and over again. Also there were issues in the past with Dropbox dropping Linux support and dropping support for Linux encrypted file systems. That didn't end up affecting me, but hearing about it after the fact rubbed me the wrong way. Another is that privacy on Dropbox has been questioned more than privacy on pCloud (according to what I've read.)
I am still using Dropbox (free account) for Joplin so it isn't like I am completely against it. Dropbox seems to be more compatible overall in many situations than pCloud and that is why I still haven't purchased a pCloud account.
To be fair, I need to do more investigation but for now what I have is working so I am going along with what I have.