On a mk5 it makes no difference which on you use,
Basically a Dump valve releases the pressuried air after the turbo to atmosphere (straight out to the air) hence the hiss noise
Diverter and re-circultion are the same and the release the pressuried air after the turbo back into the intake side,
Both are designed to stop the turbo from stalling due to the pressure build up after the throttle body shuts.