It's contradictory to ask which type was better in "adult games"
You mean the adult genre
Visual novels or books are fine, they have very little to fuck up as long as the author actually bothers to put out quality work
Animation is expensive so it's rare that a work will actually make it
Video games certaintly give you the most options, but there is a shit ton to fuck up, game to story integration, gameplay, gameplay loop, mechanics, difficutly balance, even a single one of these could make someone drop the game if its done badly, while in visual novels bad art or bad writing is the only thing, you can't be bad at both unless you're mentally challenged
and books it's just bad writing, it's literally the only aspect in which you fuck up
Sure it's expansive, but i think anyone can put out mediocre piece of adult fiction if they just sit down and fucking think for like 5 minutes, and check for errors