Both, since a diversified portfolio will almost always beat one that stacks all the chips on one side of the board.
Think of roulette, if you bet on Red, you win a bit less, but you have a pretty darn good chance of winning, whereas if you bet on number 5 you have a 1 in 36 chance of winning, but you win big if it hits....
But face it. 1 in 36 sucks.