terran is best because they are always the best in any situation. *grumble grumble*.... they are the best at defending their base, which makes the enemy not want to attack you and pick a fight with someone else. tanks, turrets, and thors... no one will get into your base, and you can build up quite a force without being disturbed. That is what terran does and it works.
play zerg and see how wrong you are. Zerg requires a much higher APM to be able to be equally effective as Terran. Zerg by default has to have more bases. Everyone who knows anything about starcraft knows that. That means that zerg needs to macro more to do the same thing. We need to spend more money.
zerg, they are naturally the "takeover race" basically meening like the previous post says they require you to constantly expand. But with the expansions so comes the creep and horde of forces
that forces you to be active though. You have to fight while another player might sit back and tech up. Your constant fighting with lings banes and roaches isn't going to touch a thor/bc/tank army.
Of course T1 and T2 units won't be able to do a whole lot againt T3 units. I don't really see the point you're trying to make here. Further, zerg can produce every single units from one building, the hatchery. You only have to hotkey your hatches to be able to make everything. Protoss and terran don't have this advantage, since they have to individually hotkey and monitor all their queues on production buildings. Zerg is actually more easy to macro with then other races once you get the hang of it. And once you do, you can easily start to vastly outnumber your opponents as your race is supposed to. That's where the zerg gets it's advantage from. So stop underestimating/bashing it please, as you clearly don't know what you're talking about. Or at least don't have enough experience with it yet for your arguments to hold much truth.