It isn't the voltage or the current that matters (at least until the voltage starts arcing which will cause severe burning), it's how much of it is absorbed or passes through the body. A Human body has electrical resistance which tries to prevent current flowing, the current it can actually pass depends on how well the contact is made to the body, the resistance of the path it flows through (could be across 1mm of skin or from head to toe) and how much voltage is there to 'push' the current through. Higher voltages will 'push' harder so are potentially more dangerous but through a low resistance body path even a small voltage can do harm.
Example: Take a small 9V battery, the type with two terminals on top. Place a finger on your left hand on one terminal and a finger on your right hand on the other. 9V is there but you will not feel anything. Now place the same terminals across your tongue (remove your fingers from them first!) and you will get a nasty tingle. The same 9V is there but the path through your tongue allows a higher current to flow than from hand to hand.
The amount of power available is almost irrelevant, it's only the amount that can pass through your body that matters. Analogy: Which is more dangerous, having a 100Kg block of concrete dropped on your head or having a 100Kg block of feathers - answer, they are equally dangerous.
Brian.