It depends on crop or FF. On my 40D I actually prefer the 50mm for portraits. 85 on my 5D2. 85 is good for headshots on the 40D but unless I have lots of room to step back, I often find it difficult to get half to full length shots while indoors. Outdoors is fine, but then I'm having to speak loudly to my subjects. I use the 70-200 (f4 IS) for portraits at weddings. The 24-70 is good for portraits on a cropped body too. Funny thing is, I've used all of those lenses for portraits, even my 100mm macro. There is a general rule of thumb for the 'best portrait range', but really, in the end for me the best portrait lens is the one that I currently have on hand to take the portrait with.