First, the 24 is a superlative lens. It is, in fact, my favorite. It is my go-to lens for anything outdoors, and I'll use it for anything else if I can think of an excuse to do so.
That writ...if I were looking to do a panorama, it's not the lens I would pick. Shift panoramas just aren't all they're cracked up to be.
When I got the lens, on a lark, I did a shift panorama in all four directions. The field of view was almost identical to that of the 16-35 at 16mm, but the 24 simply stomped all over the 16-35.That is, at extreme shift in the corners, the 24 is still sharper than the 16-35 in the corners.
However...I just did a quick experiment, the results of which aren't worth posting. I did a two-frame handheld shift panorama of my back yard, with the camera in landscape orientation. Then, I grabbed my Shorty McForty and did a five-frame handheld pivot panorama, this time with the camera in portrait orientation. A quick trip to Photoshop, and, after correcting for geometry, the resulting usable field of view was essentially the same. The results with the Shorty McForty not only were visibly much better at "fit to window," it had about half again as many megapickles.
There's no comparison, and you really shouldn't expect there to be one. As amazing as the 24 is, it's just not going to be able to compete in that kind of a setting -- any more than APS-C can compete will 135 or 135 can compete with 645 or 645 can compete with large format. And, of course, a two-row twenty-shot panorama with an 85mm lens would wipe the floor with the Shorty McForty panorama, and a four-row eighty-shot panorama with the 180mm macro would be insanely high quality that would make the 24 look like a Coke bottle.
I can't think of any time that I'd ever actually want to do a shift panorama with the 24. Any time I'd be tempted, I'd simply slip the Shorty McForty out of my pocket and use it instead.
Yet another thing the Shorty McForty has going for it: the nodal point is so close to the focal plane that you don't need a fancy panorama rig to get good results. Just pivot the camera on the tripod as-is and, unless you're especially unlucky in your choice of subject, the parallax mismatch won't be a factor.
As to which of the TS-E lenses to get...well, I really don't see any of them as exactly interchangeable. 17mm is a bit wide for my tastes for most things, though it's the lens of choice for closeup portraits of skyscrapers. For the stuff I want to take pictures of, you have to get too close for visual comfort. 24mm is the classic wide angle focal length for a reason. You're not going to find a better lens for product photography than the 90, but I'm personally holding off until they update it with independent tilt and shift. And the 45 is literally the textbook normal lens, for those who like normal. With its movements, it's a lot more versatile than any of the 50s, so long as you're only doing tripod work.