Here's a good read regarding the different versions:
https://www.debian.org/doc/manuals/debian-faq/choosing.en.html
3.1.5. Could you tell me whether to install stable, testing or unstable?
No. This is a rather subjective issue. There is no perfect answer as it depends on your software needs, your willingness to deal with possible breakage, and your experience in system administration. Here are some tips:Stable is rock solid. It does not break and has full security support. But it not might have support for the latest hardware.
Testing has more up-to-date software than Stable, and it breaks less often than Unstable. But when it breaks, it might take a long time for things to get rectified. Sometimes this could be days and it could be months at times. It also does not have permanent security support.
Unstable has the latest software and changes a lot. Consequently, it can break at any point. However, fixes get rectified in many occasions in a couple of days and it always has the latest releases of software packaged for Debian.
Personally I mostly run Debian Stable and on the one machine where I don't I run a completely different distro altogheter (Fedora). If I didn't run Fedora I would rather use Sid (unstable) than Testing.