Man, I've gone down the rabbit hole of subscriptions so many times — and honestly, it depends on what kind of reading mood I'm in. For general novels and tons of indie stuff I rely on Kindle Unlimited because the monthly fee often gets you a surprising mix of popular and niche titles, and it's perfect for binge-reading throwaway sci-fi or trying a new romance author. Scribd is my go-to when I want variety: it mixes ebooks, audiobooks, sheet music, and even articles — it feels like a buffet. Kobo Plus is great if you're outside the US; their catalog skews toward European and indie titles and the reading app is solid.
If I'm craving comics or manga, I switch modes: ComiXology Unlimited and Marvel Unlimited are lifesavers for superhero binges, while VIZ's subscription and Shonen Jump are unbeatable for straight-from-Japan manga releases. For audiobooks plus ebooks, Storytel and Audible's subscription tiers (where available) are worth checking — Audible has audio-first perks, Storytel tends to bundle a lot of translated fiction.
Libraries are underrated: Libby/OverDrive and Hoopla let me borrow ebooks and audiobooks for free with a library card, which is a serious steal if your local system participates. For tech and professional reads I keep an O'Reilly (formerly Safari) subscription on hand — it's a different beast, more classroom and reference oriented. My habit is to try the free trials, see if my favorite authors are in the catalog, and then stick with one or two services. It saves money and keeps my reading queue delightfully chaotic.