Both types of sports are good to learn something, and, obviously to live million of adventures. If you takes a lot of time in these sports, you will be a proffesional in any type of sport.
First, I would choose an extreme sport because it gets more risk and you can live feelings that, maybe, doing a conventionnal sport you can't get it.
Beside of this kind of sports are very originals because they are practiced by a few people in the world, while the conventionnals sports are and ordinary thing that are practiced by a lot of people.
Although I'm choosing extrem sports, I think that the other kind are very beneficial to the rest of the people who want to do something normal and be entertained and healthy.