I have a strange affinity to grain appearance. My limitation is that I do not have a darkroom and all my photos, even the printed ones, come from scans. Grain has a huge impact on the final appearance of scans. I am not into super-smooth results, I like grain and texture, but I need grain to exhibit the certain quality that I call tightness. Think of it as a combination of uniformity of size, placement, and grain contrast.
When I got back into film, I quickly learned that people on forums and social media have different requirements for developers that do not apply to me. For example, when people say fine grain, they usually mean blurry grain, not smaller grain. The finest grained developer in my mind is Rodinal or Ilfosol3, because they keep grain its natural (smallest) form. Even Ilford for some reason recommends DD-X for "best overall quality" with all of their films, even though it delivers awful grain tightness.
So... I experimented, and quickly discovered that D76/Xtol are almost perfect. I treat them as almost the same developer in my mind, because they're much closer to each other than anything else. Out of those 2 I prefer Xtol because it lasts forever and is perfect for infrequent development sessions.
However, when I need PERFECT grain tightness and I don't mind sacrificing shelf life or convenience, I reach out for Ilfosol 3. I discovered Ilfosol almost by accident, and I'm blown away by its grain quality. It has never gone bad on me, but that's because I've been super careful consuming it quickly being under influence of the advice I found online.
And finally, once I started shooting large format I had to adopt rotary processing. Grain is not an issue there, but I am not comfortable reusing developer with rotary agitation, so I needed a last-forever one-shot liquid (because I shoot very little of LF). Ilfotec HC was the obvious choice by being the most available HC-110 equivalent.