The American Community Survey (ACS) replaced the decennial long form beginning in 2005. While the subjects are very similar between the ACS and the decennial long form, the survey methodology is substantially different.
Maki images courtesy of Mapbox
American FactFinder has only the most recent years of its surveys; Social Explorer and NHGIS have all the population ones back to the first one in 1790.
American FactFinder has ALL available geographies (except block groups for ACS data prior to 2013); Social Explorer and NHGIS have block groups for all ACS years. NHGIS has all geographies. Social Explorer may not have some less common geographies.
American FactFinder has all available variables; Social Explorer doesn’t have variables that involve some suppression. NHGIS is working to include all but is a work in progress.
Social Explorer and American FactFinder both have this capability; American FactFinder is harder but has some variables (from current surveys!) that Social Explorer does not.
Only NHGIS allows download of shapefiles for use with ESRI mapping products.
Only DataFerrett or IPUMS* provide access to public use microdata sample (PUMS) data (but the only available geographies are public use microdata areas [PUMAs], super-PUMAs or higher levels of geography, e.g., states).
Only DataFerrett* allows you to create your own, but only with PUMS data, so only with PUMS geographies.
American FactFinder has most of the (current) Bureau surveys; Social Explorer has all of the decennial population surveys, 1790 to present plus a few other things; DataFerrett* has decennial and ACS data, the Current Population Survey and a few other Bureau surveys (SIPP, SAIPE, et al.), plus non-Bureau data like the Home Mortgage Disclosure Act data; the National Survey of Fishing, Hunting and Wildlife-Associated Recreation; and much more.
Social Explorer doesn’t provide margins of error (MOEs) with the data. If you need to be extremely precise, get data from NHGIS or AFF to be able to evaluate the MOEs.
*If you need help, see contact information above at right for the Librarian for Numeric Data Services and Data Management.