every BI tool has its own strength as well as drawbacks.
For eg in qlikview we can able to access data by just opening QVW file there is no need of continuous db connection like cognos.
Drawback like there is no write back to database
It seems very difficult to tell u answer to this ques.
Any BI tool should be
Easy to use
Easy to learn
If you want to do some new changes it should not be time consuming mean u can make changes easily and qlickly as per requirement
It should not too costly
It should able to connect multiple data sources without any problem.
Response time should be better
Because after creation of any dashboard end user at least should have some idea how to handle it.