If you are new to painting, maybe taking your first class, when you go to your local art supply store you will find many kinds of paint - oils, watercolors and acrylics are the main types. Each type of paint has several manufacturers. For example, Grumbacher and Winsor & Newton both make oil paints. Most manufacturers have several lines of a particular type of paint - Winsor & Newton Artists' Watercolor or Winsor & Newton Cotman Colors (also watercolors).
So what do I buy?
The main thing to understand when buying paint is the difference between student grade paint and artists' grade also referred to as professional. Artists' grade paint is usually marked as Artists' Watercolors or Professional Acrylic Artist Color or Artists' Oil Colors. Student grade paints or any paints of a lesser quality are rarely marked as such. It will be obvious however when you compare the price of $7.14 for a 5ml tube of Cadmium Red Winsor & Newton Artists' Watercolor (artists' grade) to $2.98 for an 8ml tube of Cadmium Red Winsor & Newton Cotman Colors (student grade).
So student grade is more economical?
Maybe. Maybe not. Whether you are working in oils, acrylics or watercolors, the artists' grade paints have a higher concentration of pigment and therefore produce a richer more intense color. So it is possible - and I find this especially true with watercolors - that you will use less paint when working with artists' grade.
But what if I'm a beginner?
If you are truly a beginner perhaps student grade is the way to go. If you have an on-going interest in painting or you regularly take art classes, try to buy the best your budget will allow. Otherwise you may find yourself frustrated by not getting the results you see other artists getting. I have watched some students become so accustomed to using student paints that when they tried artists' grade they had trouble. The color is so much more concentrated and intense it's like learning the medium all over again. Some even switched back to student paints and while their work is good it lacks color punch - like a weak cup of tea. On the other hand, some people like weak tea. Personal preference is certainly part of it (just remember that you need to master the medium not the other way around).
If you are hesitant to put down a small fortune for art supplies or don't have a small fortune to put down, buy student grade and replace it tube by tube with artists' grade as you can. If you are taking a class ask your instructor for his or her recommendation and buy a few artists' grade so you will be aware of the difference right from the beginning. And finally, remember that whatever kind of art supplies you buy, if you take care of them...in other words don't leave tubes of paint on your dorm room floor for your drunken roommate to step on...they will last for a long time (but the roommate is 50/50).