The distinction between a Doctor of Science and a PhD or Doctorate of Philosophy is more one of terminology than substance. The diplomas are considered equivalent degrees and are usually viewed equally when seen on a resume.
Therefore from a practical standpoint there is very little difference between the two degrees. Neither degree is better or worse than the other.
The major difference is that a Doctor of Science usually denotes study in a scientific field. In many cases, the difference is the term that a school wishes to put on its degrees. In some schools a PhD is considered a liberal arts or a social sciences degree while and ScD is considered a hard science degree.
Online PhD and doctor of science outside and inside the US
Something to be aware of is that outside the United States, a Doctor of Science degree is the generally rewarded degree. In many cases it is the degree awarded to medical doctors and others.
In the US, PhD and ScD are often interchangeable. Different universities may award a PhD or a ScD for the exact same course of study. Many North American schools simply call all doctorates PhDs.
Masters, ScD and Online PhD
One distinction that is sometimes found is that a ScD or DSC is awarded when a candidate has not completed a master’s degree. At many schools, the PhD program is only open to those who have completed a masters’ degree.
Persons without a masters’ can enter the doctorate program but they will be rewarded the ScD instead of the PhD. This is the case at many law and medical schools for example. In some cases doctorates are awarded to students who completed a special course of study to prepare for a career in a particular subject such as law or dentistry.