When it comes to selecting windows, there are many factors to consider. Their style - or the way they open - is just one of them.
It's important to take into account the way the window operates. Bay windows are usually a bad choice, while casement windows are the best to minimize air leakage.
Anyway, do not forget the fundamentals.
More important than small differences involving the style and the opening type of windows are issues such as the type of glazing, the number of panes, the materials that make the frames, thermal breaks, and so on. See: Selecting the best residential windows for cold, mixed and hot climates.
Types of Operation
We can consider four main opening types of windows:
1 - Fixed-pane windows ;
2 - Double-hung (vertical sliding) and gliding windows (horizontal sliding);
3 - Casement windows, hopper windows and awning windows (they differ on the location of the hinges: on the side, on the bottom or on the top of the window).
4 – Bay and bow windows.
Fixed-pane windows don’t open, and their advantages are obvious: they are excellent for natural lighting, less expensive and the best to minimize air leakage.
But they do not allow ventilation...
Sliding windows - double-hung and gliding windows - are variations of the same frame design. They feature (two or more) sashes, with at least one of them sliding horizontally. They are leakier than casement windows.
Casement, Hopper and Awning Windows
Casement, hopper and awning windows are variations of the same frame design, based on hinges at their side, bottom or top.
Their compressions seals make them very effective at air sealing. Casement windows are the best option for energy savings and cooling strategies with breezes.
Bay and Bow Window
Bow or bay windows are projected outward... They are good for views, natural lighting and ventilation. They may allow a higher sense of spaciousness, and are common in kitchens.
But their design reduces their structural strength and makes them more maintenance-intensive and prone to unwanted heat loss and to overheating and glare problems, and also to water condensation and air leakage. Avoid this type of windows.