Should I use a Ridge/Soffit vent or Attic Fan?
Before I added my ridge vent when we had consecutive days of 100F the attic could get up to 120-125 easy - and my roof is heavily shaded.  I would come down completely soaked - like swimming pool soaked - when doing 15 minutes of electrical work.  

I just added a ridge vent to my attic a few months ago.  Measured attic temperature after a couple of days in the high 90s and the high temp was around 7PM at low 90s but basically it stayed in the mid 80s.  So 25F temperature change, being conservative.

We did cut out 3 inches on each side of mine so a total of 6 inches.

I am not sure what an attic fan would do in comparison.  The air needs to get out of the attic. Hot air will escape upward.  The attic fan will take hot air out of your house and put it in the attic, with no where to go.  I could almost see the attic fan as barely making a difference due to the heat introduced from the component in this situation.  And from an energy stand-point it doesn't make sense to run something that is a low difference maker.  In this situation I could see just using your AC as being more efficient.

You would ALWAYS put the ridge vent before the attic fan.  Now would you want to install an attic fan with the ridge vent is a really good question.  I could see the benefit of having the attic fan going with the hot air having an easy escape route.