We all know that wood windows require many hours of maintenance, and the end result is always flaking paint or rotting sills:

Wood windows do not have an internal drainage system, meaning the water has to pass over the frames to drain.
Fibreglass windows do have an internal drainage system but the corners of the frame are screwed and caulked together. This means that through expansion and contraction the corners will open up, resulting in air and especially water leakage.
Aluminum Windows have the same corner leak problems as Fiberglass, as well as being colder.
Vinyl is the most durable product with very little maintenance. All corners are welded together, leaving no chance of leakage.
However, not all windows are the same! Look carefully at a cross section of a vinyl window frame. Count the number of chambers, and note the thickness of the chamber walls. Multi-chamber construction is crucial; the frame must be able to properly support the glass. Also, the more chambers in an extrusion the better the insulation value. Avoid vinyl windows that require added steel or wood to the interior of the extrusion. This is usually an indication of a weak extrusion.