Since I shoot bands and people in indoor venues, often not well lit, the 70-200 f/2.8L (the non-IS version) is what I shoot most pictures with. People tend to react positively to "head and guitar" shots and to facial close-ups and the 70-200 range on a full-frame (5D Mark III) works extremely well, since I can get the shots without having to be so close, so people's facial expressions are usually natural. Many people don't like having a camera so close to them. When I used a crop (T2i), I used the Sigma 85mm f1.4 for my "head and guitar" and general photos of people and the Canon 135mm f/2L for facial close-ups. When I switched to full-frame, the seldom-used 70-200 f/2.8L became my most versatile lens.
Canon: 28mm f/1.8, 50mm f/1.4, 100mm f/2.8 L IS macro, 135 f/2L, 200mm f/2.8L, 70-200mm f/2.8L (non-IS)
Sigma: 85mm f/1.4