They are all b&w film developers marketed by Kodak, and by now likely made by Champion.
HC-110 in the B dilution is awefully like d-76 at full stock or 1:1 use to my eyes. HC-110 has the convenience of a liquid concentrate with a quite long life. Not like Agfa Rodinal long, but a few years anyway.
I have not played with t-max or xtol developer - they are 'newer' than my experience in photography, and I am mostly happy with the old dogs.
Tmax films (tabular - or flat if you will -silver crystals) are much more suceptible to development variations than traditional (cubic -or non flat silver crystal) films. So Tmax might work easier on them, or at least be marketted in that manner.
I think Xtol is a more advanced ie. more modern (although 20 years old) ascorbic acid based developer.
I have never felt the need to use it, altough I must say this is most likely because I usually mix my own developers from scratch.
I have played with vitamin C based developers, and they can make nice negatives. Pat (gadget) gainers PC-TEA was handy like hc-110.
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