What mode is your camera most often in? Why?

Mr 251,

Aperture priority for landscapes if you are satisfied to let the camera do the initial judgement of exposure rather than using more manual control.  As others say, this gives you control of the depth of field (DoF) although you do need to have some idea of what DoF the camera has at various apertures.  It isn't that obvious on an LCD or through an EVF, for example.

The EV control is used to dial-in any exposure compensation that may be appropriate.

As another poster mentions, you need to ensure the shutter speeed is known in case it drops too low, risking camera shake or even blur from wind-moved stuff in the scene; or from other moving elements.

There is another reason that I don't think anyone has mentioned so far in this thread (forgive me if someone has): forcing the camera to stay at your chosen aperture setting means that you can make sure that aperture is as near to the lens' "sweet spot" as possible (after DoF considerations).

Most lenses will suffer at their widest aperture - usually at the edges/corners.  Most will also suffer as the aperture is nearing it's smallest because diffraction effects begin to confuse the light rays as they transit past the edges of the wee hole.  The diffraction problem is particularly evident with cameras having the smallest sensors but it happens with vitually every lens/sensor combination at some point.

Landscapes often contain a lot of fine detail; elements of the composition at the edges and corners are often just as important as the stuff at the centre of the picture. Using the lens sweet-spot lowers the risk of lens issues lowering the IQ.

SirLataxe