How to decide which martial art to learnIf you plan to strengthen the core, I'd say Judo and Brazilian Jiu Jitsu are very good for that. Most of these martial arts I mentioned below exercise your mental strength and discipline. For self defense purposes, I'd choose the striking ones over the grappling ones, but that is my personal preference.
I would classify the martial arts as follows: 1) Striking x Grappling; 2) evolution oriented x tradition oriented;
Here are some examples:
Judo: Grappling and tradition oriented
The objective of the martial art is to make the other person fall or imobilize him for a period of time.
Some rules have been changing as it is an olympic martial art... like types of grabs, making leg picks illegal, stopping extended periods of ground fighting. I'd still put in the "tradition" bucket though, because it is a very old martial art. It's a beautiful fight.
JUDO: THE OLYMPICS, RULE CHANGES, JIGORO KANO, RYOKO TANI AND THE JEWISH GRANDMOTHER