I did try out PanDebian for a while.Usually you update everything at once in Debian. I don't doubt there is a way to update only a package and it's dependencies (and the dependencies' dependencies, etc.), but that means it will probably update most of the system anyway in quite a lot of cases. Don't know how you could do that in any other way unless you started having multiple versions of the same dependency and I don't know why one would want this.I use Arch on my desktop PC and I like it, but I don't really want it on a portable PC. If you don't stay up to date with the bleeding edge, you will undoubtedly have many problems with Arch. Stuff breaks all of the time and a lot of the maintenance is left to the user (and this seems to be getting worse over the years). I also dislike the fact that its package management system doesn't support partial updates (you want to reliably update something? Have to update everything. No clue if Debian is the same)
As soon as there was a LibreOffice update synaptic told me and I could update.
Synaptic can look for packages that got an update.
Then you can select all updates.
If you use the unstable packages then you should get quite some updates I suppose.
(Arch user myself)