Mikey,
It is really a matter of personal preference, goals, materials, and PRACTICE! Some modelers brush paint everything. They develop their techniques, practice with their paint of choice, and come up with results they are happy with. Some modelers, especially automotive builders, can achieve great results with spray cans. The availability of many different colors, types of paints - hobby, automotive, general purpose paints, etc. can be a real bonus. With a little practice, you can achieve great results. The larger scale of most auto models makes use of the spray cans possible. Most automotive paint schemes use one or two colors. There are many good articles on the steps involved in acheiving success with spray cans. Other modelers, especially those building in smaller scales, prefer the control of an airbrush. Airbrushes allow you to control the amount of paint that you apply to your model. They also allow you to use custom mixed colors, apply different techniques, etc. As with any tool, they require practice. Many modelers are intimidated by airbrushes. Patience, planning, and practice are the keys. You will find hundreds of articles on this site as well as other sources on indiviual opinions on what airbrush to buy, what paint to use, what pressures to spray at, etc. Choose what information you wish to start with, and just practice, practice, practice. Don't be discouraged. You can use empty water or soda bottles to practice on. play with different settings, see how each effects the results. Good luck, and remember HAVE FUN! This is a hobby.
David