I went with the TS-E 24mm f/3.5L II. TS lenses correct perspective distortion and allow you to alter the DoF - but they don't alter the angle of view. So, ultimately you need to pick a focal length based on the usual criteria for such a choice. If you want to shoot wedding rings, the 24mm is not the best choice, if you want to shoot church exteriors, the 90mm probably won't work for you.