Once a person decides to use DNA genealogy in combination with their conventional research, the question usually is how many markers should I test?
The simple answer is the more, the better. The real answer depends on what you want to learn from your test as explained below. Generally, it is recommended that you start with a 25 or 37 marker test if you plan on using the test to help with your family's genealogical research. All tests from 12 on will determine theidentity of the ethnic and geographic origin of the paternal line.
12 Marker Test - Will help identify the ethnic and geographic origin of the paternal line and may be sufficient in proving relationships within a surname with a solid paper trail.
25 Marker Test - Better insight and more definitive in helping refine the time frame of when the common ancestor occurred.
37 Marker Test - FTDNA's recommended test for tracing the male paternal ancestor for genealogical purposes. The additional markers also help refine time frame even more.
A 67 Marker Test is also available for serious genealogical research. To make any determinations you must have another member that you match tested at the same amount of markers.
Basically, you can start with what you can afford then upgrade at a later point in time. When you order a test from FTDNA and join a project at the same time, there is a discounted price.