Crampon choice is dictated by your boots and the terrain you intend to cover. Conveniently, crampons and boots are classified into three categories so you can easily match the correct crampon with your boots or vice versa. For example a B1 boot (flexible walking boot), would require a C1 crampon (probably a flexible 10 point crampon). A stiff B3 mountaineering boot would normally require a C3 crampon.

More on crampon and boot classifications.

Other considerations when buying crampons are the binding type and the number of points.  Walking crampons generally have a strap binding that does not rely on heel and toe bails normally found on C3 climbing crampons.

Kahtoola make very light crampons that can be fitted to approach shoes or light boots. These are useful for lightweight travel were you might have a short snowy section to negotiate and should not be purchased as an alternative to a proper walking/mountaineering crampon.

More on Kahtoola crampons.