So far HR-T is the only one I've used, since typically I do two to eight or ten shots per year for Worldwide Pinhole Photography Day and that's about it. My current box is running pretty low, so maybe I need to learn more before restocking.
I was under the impression (and I'm not sure why) that HR-U
replaced HR-T. If that's not the case, I would appreciate knowing what the differences are between the two. It appears the RX material is blue sensitive.
Hmm -- a little searching turned up
a Fuji page on their medical Xray material. It lists RX, HR-U, and HR-T for which the "specifications" seem more qualitative than quantitative but suggests the HR-T may be higher resolution and higher contrast.
You now know everything that I know!