Well, you might want to take a look at:
- The responses where you posed a similar query previously.
- The same question asked to Mac Automator.
- Compare the list of BTT Actions to the list of KM Actions (note also the support for plugins).
- Compare the range of trigger mechanisms available between the two apps.
For me, BTT is for manual triggering of actions, and typically ones that are relatively simply or self contained; though sometimes they can be complex scripts that are called.
KM on the other hand deals with a wider range of triggers, and alongside Hazel, has me covered for my own unattended background trigger needs. It also allows me to make use natively of actions and functionality that BTT does not naively support - see the listings referenced above.
Hope that helps.