I’d say that my favorite inanimate TF’s tend to not involve making someone into a conventional object of some variety–turning someone into a toilet, or a piece of clothing, or anything like that. Rather, the style I much prefer is manipulating, dismembering, and altering someone’s body until they are little more than an object, and yet still alive. I’ve written a few stories like this, such as my “Living Latex” stories and captions, and “The Trophy”–another example would be some of the scenes from Tagame’s manga “Zenith”.
That said, my favorite sort of form that I could inflict on someone I hate, within that genre would be something like this–assuming I could manipulate their body in any way, while keeping them alive. First, remove their arms and legs. Ideally, this would be done slowly over an extended period of time with a device like a very sharp grater or peeler–removing small layer after small layer, and allowing them to heal over between each treatment, slowly reducing each limb down until all that remains is scar tissue. Beyond that, what came next would depend a lot on the individual person.
In any case, it would involve destroying whatever part of themselves they were most proud of. If they were proud of their muscle, I would probably force feed them until they were a massive blob of fat, seal up their body, and use them as a bean bag chair. Proud of their cock? I might nullify them entirely, or manipulate their cock until it was something completely useless–perhaps several subincisions to divide the shaft, and then a few rigid silicone injections to force them into impossible, artistic position. Sensory deprivation would be key as well–removing their eyes and ears, perhaps moving their brain and nervous system deeper into their body so that the head and neck can be removed entirely.
So yeah, something like that. Alive, once human, but now, their body ruined and useless for anything beyond what I have designed them for.