Which is the best team in history of IPL? Mumbai Indians or Chennai Super kings?

Chennai are one of the most successful team as they have reached playoffs every season. However, they are always under pressure and underdogs when they face Mumbai Indians. Their head to head record is 12-18 with MI ahead of CSK by 6 wins and that’s the interesting part. Futhermore, MI has 4 straight win streak against CSK in their last 4 matches.