Online play seems to be about overwhelming. I'd play zerg every time
All about build order mastery. I was a Marines/Marauders player in WoL.
Zerg rush works, but its an all or nothing tactic and timing is critical. Seconds too late and your opponent has time to get enough units to repel the rush, you're done.
Most of the Bronze league 1v1 games are all about build order. Every once in a while in 4v4 my group of buddies would find players willing to really get into some of the tech tree. But I rarely had time to get Medivacs before the game was over.