is that one has at least three excellent lenses to choose from that will do the same task.
The 100mm is a wonderful lens with great color rendition and sharpness. It can be used as a macro or as a short tele. It was my very first lens and still my be my favorite.
The 77mm is a classic and no one would ever argue against picking it. I don't have one, but I do have the:
70mm, which as good as any lens for portraits. And sharp? My word it is sharp. I just recently did portraits of an older women. I shot at f/11 to get consistent sharpness, but I'm beginning to think that may have been a mistake. Every nuance of skin tone is visible, and that requires major PP. Fortunately, I have a pretty good soft filter plug in, but still I can't jack it up enough to hide what needs hiding without getting fluffy looking. A soft filter lens seems like a good idea. Here are a couple of examples from the DA 70mm f/2.4 Limited:
(The first image was taken at f/2.4, ISO 1600.)
And a couple from the 100mm. The first is a bit jacked up contrast wise for effect. The second is an old favorite.