SWIM's always found harmine to be fairly stimulating but understands that it's actually harmaline that makes one sleepy/dreamy.  THH is more centered, like something between a mild psychedelic and a nootropic.  69ron's posted his account of the difference between the three here:  Harmala alkaloids for beginners? - Harmalas - Welcome to the DMT-Nexus.  SWIM finds it to be quite accurate, though he has little experience with harmaline itself.  The difference between THH and the other two is that THH lacks the mental cloudiness commonly experienced with them.