I like polished diorite and raw andesite the best. Raw andesite is very close to gravel, which is nice when you get sick of the gravelly footstep sound. Polished diorite looked nearly identical to acoustic tiles, particularly of the style I saw in school buildings in my childhood.
I really like polished Diorite for some designs. It looks good together with polished Granite. I sometimes use them together In a checkerboard pattern. Andesite is very useful in combination with stone, cobble and gravel for making walls and rustic gray paths that shouldn‘t look too uniform. Diorite and especially granite can be used to increase the diversity in paths as well.
If I go by looks alone without thinking of how the blocks will be used, I like polished diorite the best and find Andesite uninteresting.
Personally, I've never used either of these stones in my builds, mostly because I just don't know how to make them fit in my building style. I tend to build more fantasy or medieval build (Wizard towers and castles). I never know where to place these stones or what blocks to use with them. In my opinion, though, I like andesite and diorite. Diorite reminds of marble, a block I would use all the time in tekkit classic, and I like andesite because of its dark stone-like texture.