Brawl by a country mile.
I've played quite a bit of SC4, and while it was fun, it suffered from the same flaws as SC2 - the entire single player mode can be beaten by mashing a single button, as can all but the best human opponents. The characters weren't balanced and certain moves pretty much impossible to counter/stop.
If you try button mashing in Brawl you get your ass handed to you by even a low level cpu player or someone who's played a few matches







