I'm sorry but that particular comment is referring to shifting a normal lens, when a rail for panos is definitely required to avoid the different perspectives from moving the camera. I'm not sure you are getting the idea about what the shift function on a tilt+shift lens actually does. The camera stays immobile, but the lens element is shifting across the sensor and utilising the full image circle. You manually focus your first shift shot. On shifting the lens for the next shot you do not touch the focusing ring as the focus remains constant.
Sorry, Peter, but you're incorrect. A shift-pano with a TS lens, where the camera isn't moved but the front of the lens is shifted relative to the camera, will
result in parallax. Whether or not you can see that in your image depends on the relative distances to and between the subjects in the image. Old view cameras shifted the camera back with the lens fixed in place - no parallax. TS lenses used as you describe shift the lens with the camera fixed in place, and that means parallax. To avoid that, you need to either fix the lens in place for an optimal solution (DIY collar or the expensive Hartblei one), or use a macro rail to move the camera an equal-but-opposite distance as you shift the lens.
It's also worth mentioning that for architecture shots using a shift pano, for example, if 24mm isn't wide enough to capture the full height of a building, negates perspective correction - and that may be the very reason you used a TS lens. So, to the OP - the primary determinant of 17mm vs. 24mm should be the focal length you need. A sharper lens (TS-E 24L II) doesn't help if you have to cut off the top and sides of a building.
Personally, I went with the TS-E 24L II as that focal length works best for my style.