I bet that increasing the environment light's strength looks way better than using a second sun.
Sorry, Klaus, I had to write this, since this has been discussed quite often.
Maybe it's a matter of taste, but using a second sun might be good for a scene with... well, two suns. To me the lighting looks quite flat, when a second sun is used to lighten up the scene.
So why not using the (more or less!!!!) real thing?