Neither! Ridge vents and turbines provide attic ventilation not insulation.
Which one works best depends on whether your attic ventilation system is balanced or not. Per the International Building Code,
- a ventilation system should provided and a net free area of 1/150 of the area of the space ventilated
- except that reduction of the total area to 1/300 is permitted,
- provided that at least 50% but not more then 80% of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet above the eaves or cornice vents.
Ridge vents work by means of natural convection. If the required air intake is not provided they will not perform per the manufacturer's specification.
As for turbines, they provide suction created by their rotation which is wind driven. Again if proper air intake is not provided they too will not perform per the manufacturer's specifications.
Begin by calculating the required ventilation per code and if possible calculate the amount currently installed. Increase if necessary soffit venting and roof venting to meet or exceed the minimum code requirements.
By following these steps, and the ventilation manufacturer's specifications, either one of these systems will perform as required.
For more information:
Read "How effective are the different attic ventilation methods? I read mixed reviews, and many have a commercial bias." a Q&A answered by Danny Kelly.