Man, I've bounced between so many of these. The definitive one for me remains 'Shosetsu', it's open source and pulls from a ton of aggregator sites, but the setup is a headache. You need to manually add source repositories, which feels like programming homework. Once it's running though, the customization is unbeatable—dark mode that actually works, fine-tuned font controls, and a really clean offline library.
For zero-fuss reading, I reluctantly use the official 'J-Novel Club' app. Their subscription is pricey, but you're getting clean, legal translations the minute they're done, often with translator notes. I tried 'Tachiyomi' forks for a while, but the extension ecosystem for novels is way less stable than for comics. Most people just end up on websites in their mobile browser, which honestly works fine until you get twenty tabs open and lose your place.