high frequency alternate current is the safest, in the sense that the skin effect enters in effect, and the current doesn't touch your muscles (or at least your hearth). However, the danger of burns persists.

The nasty thing about HF burns is that you often do not notice that something is wrong until you either smell the burnt skin or the burn starts to deep enough to become acutely painful. It is perfectly possible to burn 1mm dia hole completely through you thumb and nail by inadvertly placing your thumb over output connector of CCFL inverter without you noticing that this is happening.