Shrader is definitely a more commonly found valve, mostly because of its greater ease of use. You see them everywhere. Cars, most bikes, small tractors, ATVs and other vehicles. But, as we mentioned above, Presta allows higher pressure output which lets you pump the tire faster. This is good when racing.
In many cases, you might not even have to make the choice, based on the fact that you will need to get a pump which fits the valve that comes on your bike tires unless of course, you plan on attaching custom or aftermarket wheels and tires.