Terran:

The Terran are the most basic race. They are by far the easiest to master, and the best choice for beginning StarCraft players. Some people may not agree with this, mainly because they prefer the Terran and are prejudice against the others. When selecting the best race, be sure to keep an open mind. Anyway, the Terran have things which we can somewhat relate to. For instance, we know what a Marine is, what a Barracks is, and what a Command Center is. We have a good idea as to what these are, and therefore understand the Terrans a little more right from the start. We also can relate more to them because we are also humans. Some people like to stick with their own race. If that's you, then the Terran would suit you fine. If you are the type of person that likes to build many units but not mass produce them, then you should consider the Terran. Their units and structures are fairly cheap (resource wise) and so are their units. You can build many units with the Terran, but you don't want to mass produce them. If you like units with fairly decent fire-power, then the Terran once again are good for you. The fire-power which their early units possess and the SCV's repair ability help the Terran player to have the most secure defense early on. If you are just starting to play StarCraft, then I strongly suggest that you start off with the Terran to get the hang of the game and how it plays. Play the tutorial in StarCraft to get a basic idea of how to play. Also, if you're the type of person that seems to always get rushed, then Terran are good for you, because their main structures can lift-off from the ground and move to another location. This will help you to stay alive longer than you normally would.

Zerg:

The Zerg are a somewhat more complex race than the Terran in that we don't have any idea what their structures are from first glance. If you are the type of person that wants to get many units FAST, then the Zerg are for you. Keep in mind, however, that their units don't do alot of damage (the consequence for being so fast to get and cheap.) The Zerg are more difficult to master, but they can get a good offense very fast; much faster than any other race. The Zerg have a large drawback at playing from Terran, and that is that you have to have Creep to build on. You have to build special structures (Creep Colonies) to obtain this Creep, and without it, you simply cannot build structures, other than the main building, the Hatchery. Although it may be frustrating to have to deal with, once you get a good supply of it, you won't need much more. Also, you can use it to choke the enemy, because the other races cannot build on this Creep. Keep in mind that other Zerg players can build on your Creep, and you can build on theirs. When building structures, your worker (Drone) has to mutate into the structure, thus being unable to mine resources anymore. Therefore, you must constantly replenish your Drone supply to keep a good flow of resources. If you don't mind having to keep a constant eye on whether or not you need more Drones, then the Zerg may suit you. Unlike the Terran, every Zerg unit and Structure constantly heals as it gets hurt. For terran, if you don't repair, your building may burn down. With Zerg, a unit down to 3 HPs can slowly heal back to full life if given the time.

Protoss:

The Protoss are by far the most difficult race to master. This is because their units are extremely expensive and take long periods of time to build. However, there is an up side to this. The units of the Protoss may be expensive, but they can dish out and take very large amounts of damage before dying. Every Protoss unit and Structure has a Plasma Shield coating around it which absorbs damage. Only after you break through this Shield can you actually begin to damage the unit or structure. Keep in mind that the Shields constantly try to replenish themselves as they get damaged, like the Zerg heal themselves. Like the Zerg, the Protoss must have something to build on. Fortunately, it is much easier to come by. Protoss must build Pylons to build around. A Pylon emits a blue field around it, and in this blue field must the Protoss build (the field is only visible when you click on the Pylons, if they are YOUR Pylons.) These are easier to remember to get, because you need Pylons to supply enough units. Unlilke the other races, the Protoss can leave a building to finish by itself. So if you are the type of person that doesn't want to temporarily or permanently lose a worker, then the Protoss are good for you. The Protoss also require that you learn their technologies. Without it, you are doomed. Protoss special abilities are absolutely essential in order for survival. If you are willing to learn a lot of new stuff, then the Protoss will do you good. Plus, if you don't mind having to spend VERY large amounts of resources on your upgrades and units, etc., and having to expand early and a lot to get the resources needed to live, then the Protoss may be your best bet. Just keep in mind that the Protoss are the most vulnerable early in the game, and are the easiest to be killed early on. But, once you get your units in, you are VERY much more powerful than any other race. If power in few numbers is you, then you must play the Protoss.