My Most Used Lens : Canon 24-105 f4 IS USM
What makes a favorite lens a favorite. Good question to which there are many answer. This is not intended to be a review of this lens but more a personal feeling for it. The most important feature of any lens is that it can gives sharp images with great color, and do it over and over again. Fast focus and hand holdability are also of prime importance. These are the main reasons that this lens has become my favorite and stays of the front of my 1D MkIV most of the time. It gets the shots I want, has a good range of focal lengths, zooms smoothly and accurately (does creep a little) and is solidly built but not too heavy, and all for a great price in comparison to say the 24-70 f2.8L.
The range of focal lengths can be used for many things from Landscapes to Portraits and is effective for both, very sharp when stopped down for landscapes and good (not great) bokeh for portraits when used wide open. It is this versatile range that make this lens a great favorite. I rarely have to carry any other as this will suit me for most things.