Falling Skies is far better than both of those other shows and I watch all three.
Revolution I have been losing interest over time though I have them all recorded. I am about 10 episodes behind.
Defiance messed up and didn't record the last episode so I am now behind by one and I don't even care all that much. It has yet to hook me though I will give it every chance.
Falling Skies is the best Sci Fi on TV right now and its not on for very long each season. When people talk of a golden age of Sci Fi? Well this is surely not it. Sci Fi is almost dead.
These days its all about Fantasy which sometimes has Sci Fi elements. Walking Dead, True Blood and Game of Thrones.