When buying new windows, you have a few different choices for both glass and frames. Different types of glass can generally fit inside any type of frame, so you don't need to be worry about being limited. If you're stuck looking between vinyl and aluminum windows, you're looking at two pretty similar styles of windows, so what you choose will likely come down to environmental and weather factors as well as customization.
Colors and Painting
If you're purchasing windows with the intent of possibly painting the frames later on, vinyl is much more difficult to customize. Many manufacturer warranties will be voided if you attempt to paint your windows, and painting vinyl a darker color has the potential to cause damage due to heat buildup. Aluminum is easier to paint and touch up if the paint ever chips to expose the metal underneath.
Corrosion, Fading and Damage
Vinyl windows are generally durable, more so than aluminum windows, and are more resistant to scratches, dents and corrosion. The tradeoff is that vinyl windows are heavier than aluminum, and that they are slightly less effective when it comes to noise reduction. Aluminum frames are often preferred for much larger windows due to the weight, especially if they are windows without moving panes, which means less to worry about in terms of maintenance.
The exception comes in terms of climate if you live in areas that get very hot and/or very cold. Vinyl windows are much more susceptible to expanding and contracting under severe heat and cold unless you make sure that your frames use good quality vinyl. This often isn't the case, which is why vinyl windows are so appealing in terms of cost – vinyl windows tend to be much less expensive than other frames. If you buy higher quality vinyl you may lose out on some of that price advantage.
Additionally, vinyl frames are often thicker than aluminum frames, which may not be very appealing depending on what aesthetic you're going for.
Energy Efficiency and Environment
Vinyl frames tend to be more energy efficient because they conduct less heat. Aluminum conducts more heat and cold, and also condensation. Aluminum frames thus often come with thermal breaks – which are made of vinyl – that end up adding to their cost.
On the flip side, aluminum windows are actually a little more environmentally friendly in that they are much easier to recycle.
If you want windows that you don't need to pay much attention to, barring any actual damage, vinyl windows generally require less maintenance than aluminum. Some of this is due to the assumption that you won't be painting your vinyl frames, but vinyl frames also don't need to be lubricated. While aluminum is easier to paint, the metal-on-metal moving parts will require more work.
For more help deciding which type of windows is best for your home, contact a window installation professional.