Daniel, the best type of attic ventilation to have is of the passive variety: continuous soffit vents along the exterior eaves and a baffled ridge vent along the full length of the roof ridge. Baffled ridge vents are better than mesh ridge vents as the mesh vents can be short-circuited if the wind currents drive directly against the vents. Baffled ridge vents deflect air currents over top of the vent and create a vacuum effect that actually pulls air out of the attic as it passes over the ridge (the bernoulli effect). When you have the the ridge vent and soffit vents in place, having any other type of roof ventilation system in place such as gables or power vent fans can short-circuit the air flow you get throught the soffits and ridge.