Because there are so many online schools it is difficult to say which is the best one.
Your best bet is to narrow your selection down to say 10 schools that you think look suitable and then research them on the Internet (and offline) to make sure they are good schools.
Off line asking business or industry in the particular industry would be a good way to go.
One main question you need to ask yourself is how businesses or industry see the school. If they don't rank it highly and having a qualification from it doesn't mean to much, then it is best to go with a different school, or you will be wasting your money.
You can also check with the State department to make sure they are properly accredited and the like!