In-game, no preference really. I could pick a favorite, but I've already bonded with individuals of those species so I'd probably just box it. That is, unless I could "reset" one of those individuals to use as my starter (like how Ash leaves behind all his Pokémon except Pikachu when heading to a new region), in which case I might lean toward Shiny Dunsparce. (There are a few others that are really tempting, but I've considered Shiny Dunsparce my mascot for so long that it seems like it should be the obvious choice.)
In an IRL scenario (or as a character in the anime), I'm leaning toward Torracat or Shiny Eevee, based on my fluffy grey cat, Ciel (my first long-term pet). Ciel might be closer to Torracat since he's technically a tabby (albeit not a mackerel "tiger cat" tabby), but his coloring reminds me more Eevee's GSC Shiny palette. (My dad gave me a box turtle (Turtwig?) over a decade before I got Ciel, but I'm not sure if I'd really consider it a pet/starter since my mom talked me into releasing it the same day.)
EDIT: Shedinja could've also been my starter. I believe it was before I got Ciel that we had our previous outbreak of periodical cicadas and I collected their shells. Freaked my cousin out with them. xD