That repository can be used to build/install a wide range of setups (server, desktop ...etc.).
If you want a solid desktop then go with oldstable i.e. Jessie. The cost of that stability (as in solid) is the packages have been around for a while (tried and tested), not the latest versions (that might be unstable). Or it might not support the latest hardware.
Stick with just the MAIN repository and don't import things from outside ... and Debian is a single stop all encompassing product. Others are much more mix and match ... often with undesirable consequences (kernel from here, one program from there, another program from elsewhere).
Understand the core Debian concept and you can see why systemD is the preferred path as that facilitates moving more into the single core.
The Debian repository is the source for many many other distros. Typically where tweaks/changes are made and parts brought in from elsewhere. That might work OK for some but shouldn't be something that Debian aspires to provide. Debian does a great job of what it already does best.
Dedoimedo wrote
As he's looking for a desktop distro to test for stability/functionality, he should be installing and reviewing oldstable versions.In my long history as a distro tester, I've only tried pure Debian twice