It is interesting to note that in the USA and the UK uPVC is the industry standard for new homes, whereas in Japan nearly all houses have aluminum frame windows. There are a number of differences between aluminum and uPVC windows.
uPVC or rigid vinyl windows have long been popular with home owners because they are energy efficient. uPVC has a high thermal resistance which means that uPVC provides an effective barrier between the inside and the outside of a house. In the winter uPVC windows help insulate a room and keep the heat in, and in the summer uPVC windows stop the heat from outside entering a room. This means installing uPVC windows, and especially uPVC windows with double glazing, saves the house owner money in heating and cooling costs.
In contrast, aluminum windows have a very poor thermal resistance. Heat and cold is easily transferred via aluminum windows between the inside and the outside of a house. That is why in the summer Japanese homes are too hot (they use a lot of air-conditioners) and in the winter too cold (the average citizen wears a jacket and hat inside at night).
Why then does the second richest country in the world use aluminum frame windows? The answer is cost and building style. In Japan a new house is usually built with a wooden frame and lightweight walls that are designed to withstand the shaking caused by earthquakes. A new house will normally be torn down after 60 years and re-built. Thus, lightweight and inexpensive aluminum windows are preferred which will last the lifespan of the building.
Aluminum widow frames are cheap and light and do not rust. They just get a dull sheen caused by oxidization. Aluminum windows are cheaper than uPVC windows and last longer (uPVC windows normally last about 25 years). However, aluminum is easy to bend and dent. As a result if not carefully treated aluminum windows get dents and lose their exact shape making it harder to open and shut the windows. This is not true of uPVC windows which are inflexible and hard.
Indeed if given a choice a burglar would much prefer to try and break into a house with aluminum window frames as they are much easier to force open than uPVC windows. Although uPVC windows cost more they provide better security.
Finally there is the issue of disposal. For years many countries have been recycling aluminum. The metal is easy to recycle and the profit made can cover the costs of collection and recycling. The same is sadly not the case with uPVC. uPVC is made from the plastic PVC which gives off dioxins when burnt. Because many uPVC windows end up in landfills at the end of their life there is a strong chance that they will be burnt in one of the many accidental fires that occur on land fill sites. The dioxin gas given off by burning uPVC is dangerous to human and animal life.
To sum up uPVC windows with double glazing are energy efficient, strong and provide excellent security. However, aluminum windows are cheaper, last longer and are easier to recycle.