I am writing a manuscript about QGIS, and I categorized the data types into 3 classes according to popularity (raster, vector, web-data). Then I separated web-data to WMS and WFS. Under the heading WFS I introduced the OpenLayers Plugin in QGIS as WMS basemap catalog, am I right?
I think a decision to use geographic data isn't a question of popularity, but a methodic question. Raster and Vector data are basic gis data structures, they can be stored locally, or web-based. WMS and WFS are something like raster-vector, but WMS is for serving raster maps or raster map layers, they are graphic representations of raster and vector data, while WFS is a feature service on vector basis. If you want a more complete structure, see this: Comparison of WMS and WFS services or this: What are the differences between WMS, WFS, WCS, WPS? Also there are good wikipedia articles on that topic, but we all know we should not cite it ;-) In earnest: Read the stuff in the www and then try to find good articles, they are reviewed, published, accepted and citable!