Use cso-vhe.fgd if you use Worldcraft 3.3, Hammer 3.4 - 3.5beta4 or any level editor which doesn't support huge descriptions.
Use cso-jack.fgd if you use J.A.C.K 1.1.1064 or newer OR any level editor which supports huge descriptions.
The models and sprites are for better viewing of the entities on the level editor.