Brain Training to maximize returns

Hi Everyone,

Australia’s ABC has recently broadcast a new series called ‘Redesign my Brain’ with Todd Sampson.

The series seeks to explore how much the brain can be improved in areas like memory and recognition. After just one month of training Todd found himself performing considerably better on tests then he had prior.
He also competed in the World Memorization Championships, and watched a bloke in Germany play 12 games of chess simultaneously without seeing any of the boards.
So other than being a fun show to watch, it got me thinking about the advantages of brain training.
I’ve had a look at some stuff like dual-n-back, luminosity, and other brain training programs, but I’ve failed to really explore how much utility such training has.

One of the memory champions was able to remember the order of 25 decks of cards in one hour. But it didn’t seem like his ability didn’t do much to improve his life beyond providing a fun and enjoyable hobby.

So I’d like to ask:

Which areas of cognitive training do you think would have the best returns in terms of life optimization?

And what do you think would be the best way to go about that training?

Would love to hear some success stories.