It is difficult to know which to use. It seems necessary to use publication types, as well as subject headings, to get the best retrieval - a cumbersome, confusing technique. It often seems necessary to supplement subject heading searching with free text searching to get optimum results. This is the search terminology used in most of the EBM searching literature. But including these methodological filters, a search strategy can yield narrative reviews, as well as systematic reviews.
Free text seems to be the best way to go here.
That is both the good news and the bad news. They are easier to search and are quality filtered. But there are problems with these time-saving databases. While exploding a term is the most effective way of getting everything on a topic, it can also get you a some things that are completely off-topic. It can be difficult to know exactly when to avoid term explosion, and when to use it to enhance retrieval.