Performance of Shapefile and PostGIS with GeoServer?

PostGIS. Geoserver documentation has the following comment:

"Shapefiles are a very common format for geospatial data. But if you are running GeoServer in a production environment, it is better to use a spatial database such as PostGIS. This is essential if doing transactions (WFS-T). Most spatial databases provide shapefile conversion tools. Although there are many options for spatial databases (see the section on Working with Databases), PostGIS is recommended. Oracle, DB2, and ArcSDE are also supported."

This isn't the whole story; even if you don't care about WFS, everything from native-sorting to the ability to create & publish PgSQL views, query performance, data security, storage...just use PostGIS.

I would like to add for anyone doing this question, which in my experience is recommended for when you plan to change, but even if the spatial data, but if just to show them (WMS) produces better (faster) to use shapefile, see this slide

WMS Performance Tests!Mapserver & Geoserver FOSS4G 2007