Inputs for system identification What effects does have a different input such as impulse, step, sine sweep etc. on performing a system identification?

I mean what is up/down side, and which one is best, and why chose one rather than the other.

For now I see the sine sweep as the most reliable for determining a system since the other ones doesn't seem to hit nearly all modes of a system. 

But what do you say? I am not an expert at all and I am a bit confused here.
Both Impulse and Step Response can help identify a system, however it might be hard to actually perform the identification. You'd have to fourier transform the response. Basically, this is only possible using digital signal processing. Using a sine sweep, the result is easily read, but the sweep will take a relatively long time.