For sheer explosive power, traditional Muay Thai (NOT kickboxing) is your friend. Results can be seen quite quickly.
For close quarter damage then look at Wing Chun. It's a system that can be learned in a relatively short span although dedication will be required as with all other styles.
If you are willing to commit a major part of your time and dedicate yourself to learning it properly then Aikido will provide your answers but be aware, it is a long journey.
Kempo is a good blend that will include some weapons training. I particularly enjoyed this one.
One of the traditional Kung Fu systems will provide you with a new obsession. The five animal system is particularly interesting.
Traditional Karate styles such as Goju Ryu, Shukokai and Shotokan will provide a fascinating hobby and facilitate good friends but effective self defence can take a while.
If I had to choose, then for self defence it would be Wing Chun followed by Muay Thai. For a hobby, then a formal Kung Fu system with weapons training or Shukokai karate would be my choice.