It takes more maintenance but lasts the longest if painted and maintained. Roofing manufacturers' warranties require a minimum of 1 square foot of ventilation for every 150 square feet of attic space for traditional systems, but only 1 square foot of ventilation for every 300 square feet when the ridge vent system is used. That is a good indication of the difference in efficiency. There are many good ridge vents on the market, and the continuous vent, as opposed to the individual roof vent, is the most effective. Continuous ridge vents allow hot air to readily escape from the roof peak.
Most manufacturers now use a durable plastic, or aluminum, to avoid rust.
If using plastic in cold climates, make sure it is rated to withstand subfreezing temperatures. Leaks from an old roof are good indicators, as are worn, battered, or missing shakes or shingles. If the fine gravel embedded in composition shingles is missing, or piling up in the rain gutter, it is time. On flat tar and gravel roofs, look for bubbles in the tar and shrinkage near roof vents. Old shake roofs may have pieces missing, particularly along the ridges.