I'd have to say The Cat Lady
, even though it does have a publisher, and by some folks' account that would disclassify it as a "proper" indie game. Why? Because I went into it not expecting much other than the shock value a couple of youtubers showcased on their channels, I knew David Firth had a couple of roles, and that was it. But, then, I played it, I finished it, and it pretty much became a turning point in my mental health condition(s). The Cat Lady is *NOT* a horror game. It's a study on depression, anxiety, loss and grief. And, I mean, sure, you can play it mindlessly, "roleplaying" an awful person, but if you allow yourself the sincerity, the honesty of playing the game while feeling empathy and sympathy for the characters in it, it's sure to punch you right in the guts. And maybe you'll leave the whole experience feeling like you're worth something, feeling like you're not as crappy a person as your paranoia might make you think you are, like it happened to me. Depending on your choices throughout the game, The Cat Lady can be an extremely heartwarming experience, despite the creepiness, despite the creepy looks, despite the violence and the (sometimes gratuitous) abuse. That's why it is my favorite indie game.
I'm entering the contest for my girlfriend, who would definitely pick any of the Blackwell titles as her favorite, games, by the way, which she bought on GOG and made her fall in love with what video games can be. If I'm not eligible because I'm entering for someone else, then at least I hope my post gets a couple people interested in giving The Cat Lady a try, if they haven't already.