Panda is the Debian version which is Deepin based on, one with compatibility with Debian and Ubuntu. Unstable (Sid) version is a pure Debian one. Panda is based on Sid with compatibility with Ubuntu versions added, so there aren't really any problems with you using one or another, Deepin isn't an "stable" system, more like a rolling release. But be aware when putting more repositories, if you add something like a complete Debian repo, you'll change the shape of the system completely if you don't prevent it to override the Deepin repos.