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What are the differences between EDAS, FNL, REANALYSIS, and NGM meteorological datasets, because I got quite different HYSPLIT results between them?

The EDAS (now called NDAS) archive grid covers the continental U.S. after 1997 and is saved at a horizontal resolution of about 80 km (beginning in January 2004 the EDAS archive horizontal resolution was increased to 40km); the FNL archive covers both hemispheres of the globe at about 191 km resolution; the NGM covers the continental U.S. prior to 1998 at horizontal resolution of about 180 km; and the REANALYSIS data covers the globe from 1948 to the present with a horizontal resolution of about 2.5 degrees latitide. Recently, the GDAS (Global Data Assimilation System) replaced the FNL data set and has a horizontal resolution of about 1 degree of latitude (~111 km). For more details on each of these datasets and their availability see: http://www.arl.noaa.gov/ss/transport/archives.html