Gotta be the 135 f/2.
For the most part I have only their new lenses now since they;ve been on such a roll of producing world beating lenses lately. (Unless maybe you count my 300 2.8 IS as old, but that design came out well past the intro of EOS, well, well past).
Main Canon lenses now are: 16-35 f/4 IS, 24-70 2.8 II, 100L, 135L, 70-300L, 300 2.8 IS L (and 50 1.4 but the AF is poorly created) (also have an old 35-70mm).
Also using Bower 14mm 2.8.