Which are better, biofuels or fossil fuels? What are pros and cons of both?
Biofuels are better (in general)
Fossil fuels are limited. They contain some harmful materials. They cause air pollution when used. When we extract coal and oil, we contaminate land and water. You can read about the pros and cons of fossil fuels in this Socratic question.
Biofuels are safer. The only problem is the question "food for people or fuel for people?" To produce biofuel, we need some vegetation. Biomass energy is not always automatically renewed by nature. It may be depleted if the environment necessary for its renewal is not maintained. For biomass to be renewable, both soil and water are necessary for plant growth. If either of these or, in worst case both of these, is depleted biomass production may decrease or even halt.
The main difference between renewable alternative energy sources (such as biofuels) and fossil fuels is analogous to the difference between a checking account that receives regular periodical (such as yearly) deposits and a checking account that receives an initial large deposit but no further deposits. The account getting regular deposits will not be depleted (e.g. biofuels). Even if you spend the present balance, more will be added later. The second account will eventually be depleted even though the timing will depend on the rate at which the funds are spent.
The total energy we may be able to produce by using biofuels is as large as the total energy globally consumed each year.