Deciding to pursue a Masters, PhD or joint/dual degree depends on a number of factors including the kind of work you want to do after you obtain your degree and what you see as your career trajectory.
It is often difficult to imagine your next horizon and that is why many people will recommend working for a couple of years once you have completed your undergraduate degree before embarking on an advanced course of study. Understanding the kind of learning you will do in each type of graduate program can also help you determine what type of advanced degree you want to pursue. As well, finding out what alumni from those programs are doing after completing their degrees and what the the market is like for jobs in any particular field can be helpful.
In general, you will want to pursue a PhD if you are interested in a career in research or want to become a professor. Many PhDs also work in private industry or government and nonprofit organizations. If you decide to do a PhD, you will spend a couple of years taking classes and qualifying exams. Then you will work with an advisor to design a research project, write a dissertation with the input of a faculty committee and ‘defend’ that dissertation research in order to obtain your PhD. Talking with PhD students and doctoral candidates can help give you a good idea of what its like to be a PhD student which, depending on the discipline, can take quite a number of years.
Many students do research Masters degrees before working on a PhD, taking some time to increase their knowledge of the field, bolster their GPA and improve their chances of getting into a program of their choice. A professional Masters degree, such as an MBA (Masters in Business Administration), MSW (Masters in Social Work), and MFA (Masters in Fine Arts), are often called terminal degrees because they do not typically lead to a PhD. Most people receiving these degrees want to enter the workplace, although many people working on MFAs do so precisely because it allows them to teach. The phrase “terminal degree” is used differently in various contexts and a good discussion can be found here.
In the last few years, many universities have started offering more “joint” or “dual” degree programs. Some combine two related Masters degrees such as MPP (Masters in Public Policy) and an MSW or a JD (Juris Doctorate) and an MBA. These joint degrees often shorten the time it would take to do the degrees separately and allow you to get two degrees without doubling the costs of graduate school. There are also programs that combine PhDs with other courses of study such as a MD/PhD or a JD/PhD, with the MD and JD being the professional degrees and the PhDs adding a more scholarly focus. Joint/dual degrees can be more cost and time effective, however, the applications can be more complicated than applying for one degree as you usually have to apply to both programs simultaneously which often means taking two entrance tests such the GRE and the LSAT.
One aspect of graduate education that students always have to consider is funding. Masters and professional degrees are often funded by the student whereas if you apply for a PhD, you are often funded by the professor you will be working with which generally happens in the sciences, or you can also be funded with teaching and research assistantships. This will all depend on the program and the discipline that you want to pursue. Again, talking with students in various programs can be extremely helpful in determining what kind of degree(s) program you will want to pursue.
For another discussion of types of degrees look here and a simple decision tree that might shed some light on the matter can be found here. However, these general discussions don’t always take into account your personal circumstances which could include family and financial obligations as well your very own determination and perseverance. Talking with those who know you well, academically, professionally and personally, can help you make some of the more personal decisions such as how long you want to be in school and how much debt you are willing to take on.