debian testing
+ just works
+ up to date
+ more stable
+ more binary packages
- partial upgrade break system
- freezes -> broken for weeks
- huge influx of packages from unstable -> potentially breaks system

debian unstable
+ stable
+ does not freeze
+ fix comes quickly
- 'partially frozen' when testing is frozen

debian testing/unstable mix
+ get missing/broken packages from another repo
- difficult to set up
- not recommended

arch linux
+ fix comes quickly
+ more vanilla
+/- DIY
- always broken in some ways
- less stable