When I first started, I was Terran because it was the most easiest to learn and versatile of the three. Then I changed to Protoss, then I went to zerg. I'm good at all three really, and depending on the map and the opponent, I fluctuate. Though to admit it, I lean heavily towards zerg because of that all-up zergling strategy that I've rarely seen anybody block. Only through a mixture of rigorous economics, heavy micromanaging, exhaustive usage of terrain, and incredible exploitation of magic and skills that I've seen block the all-up zergling swarm.
For Terran, I usually follow a path of two techs-I'll rush in bionics with three/four barracks running, while building 5/6 factories. If it is possible, I'd follow up with a few vultures with mines, as vultures are surprisingly good against early units and laying mines before hand and luring enemy units with the ruse of retreating are also surprisingly effective. There's a 50/50 chance that this will succeed, hence the construction of factories. Heavy mechanics are key for any race, and even zergs will melt against mechanics, with only a few vulnerable siege tanks and many goliaths and vultures. Building huge numbers of factories is key, you'll find that you micromanage your units too often and find not enough time to produce units or macromanage your economy, eventually leading to huge stacks of resources. I also have 2-3 separate forces instead of just 1 main force as many players do, as reserves to send or strike at weak points.
