They are all kinda in beta currently, since they are still missing some mods and bugs are still being worked out. But for working conditions would be any of the packs, but best to go with FTB 1.4.2 pack for the normal mod pack. But be warned that mods are still missing in the 1.4.2 versions, such as Redpower 2(currently un-released) and Thaumcraft 3(unknown if it will ever be in the official version due to what slowpoke wants.)
Short Version: FTB 1.4.2 is the best to go with currently for the normal FTB experience. Though they are all still buggy and being worked on.