Mosst basic rule of thumb is to make sure they are all roughly the same colour scheme. I.e. for number 4 Blue doesn't blend with the background. It sitcks out too much.As with number 3. Maybe make the text slightly thicker and add effects. I suggest go with the theme. So with number three have the words electrocuted effect. Then change the color to white or black.
I think number two is the best so far.