Ultimately the best keywords are those that have lots of competition, often in the millions, because those are the ones that are searched for the most, cause and effect people! It is very difficult to rank for those keywords, but there is a way.
When doing keyword research there are always long tail keywords. A long tail keyword is simply a phrase with the main keyword in it.
Example:
Main keyword: Computers
Long Tail: Buy Cheap Computers
Now, if you look at the competition for most any popular main keywords it is usually very high, keywords like, money, credit cards, loans, mortgage, insurance, health, cell phones, computers, laptops, cars, the list can go on and on. Ranking for these keywords is going to be a long hard road. So, what you need to do is...