God I love this game, but its taken me this long to realise that you need different tactics for every different race.
For a while I've just been going straight for the rush with banshees as a Terran but I've just now realised that I usually get raped if its another Terran especially.
What I've seen is the easiest thing to do now is as follows assuming you want to rush.
TvP = Rush marauders or reapers.
TvT = Rush reapers, drop them behind supply line and destroy all the SCVs then the other stuff.
TvZ = Rush reapers its pretty hard for them to detect or have anti-air early enough to take you out.