They are different versions of the game.
H&D Deluxe was updated and in some ways improved, in others the opposite. Deluxe is censored and has clone soldiers, they don't have different faces (SAS or Germans) which makes the game look stupid. It does have a level editor.
H&D1 & Fight for Freedom (the addon) both have different rosters of troops. They combined the games for Deluxe and ignore the addon troops.
They are both worth playing but the original is the one to play through. Deluxe is good for addon missions and modding.
Thanks for clarifying this. I was wondering why an already free DRM free game was being sold by GOG.