Which Source to Use for What:
Coverage of journals published outside the U.S. – Google Scholar and Scopus do a lot more of this than Web of Science.
Non-English language publications – Google Scholar will find more of these.
Interdisciplinary field coverage – Scopus and Google Scholar cover more journals in fields that span multiple disciplines.
“High-influence” publications – Web of Science.
Peer reviewed journals – Scopus and Web of Science. GS known to cover a lot of non-reviewed content.
Non-journal coverage – Google Scholar has more unique types of materials (PDF files, Word docs, technical reports, theses and dissertations, etc.). Web of Science and Scopus both have “some” proceedings and books but they are mainly covering journal articles.
Book coverage – Google Scholar excels at this way more than the others as it covers Google Books content along with other freely-accessible online publications.
Authors with common names – Scopus and Web of Science can easily help distinguish between similar author names.