That is really tough! I have an EF 70-200 2.8 L IS II that I LOVE for its versatility & amazing IQ (sharpness & bokeh). I just bought my first prime though.... an EF 35 L. That lens, attached to my 7D, is a GREAT lens!! Image quality, check, super thin DOF, check, AWESOME bokeh, check & all in a good & usefull focal length! So, as for now I have to say my favorite lens in my 35L.