Wit and Humour
As long as it is not at the cost of a competitor or offending any set of people. Good natured humor will always go a long way in putting a positive effect. A witty logo that includes an element of humor will never fail to get a smile on the face of the target audience thus creating a positive impact.
However, working on humor has to be done carefully else the logo may backfire in a big way in case it offends any one or is deemed inappropriate. One must take care to ensure the humor is acceptable to all age groups and to people coming from all walks of society.