Honestly, it's become a real hunt. I've basically given up on finding a single site that works perfectly for everything. The licensed publisher or official translation team's site is often the best bet for structured, full-chapter reading without pop-ups, but their libraries are limited to what they hold the rights to. For older or public domain stuff, Project Gutenberg is the gold standard—no ads, clean formatting, downloadable. But for ongoing web novels or newer serials, you're often at the mercy of fan translation sites, and those are a mixed bag. Some are decent, some are riddled with redirects.
I've had better luck lately using the apps from bigger platforms, even if you're just reading free chapters. The experience is usually more stable than their mobile websites. Still, 'flawless' is a high bar—even official apps sometimes have wonky formatting on certain devices. My current compromise is using an ad-blocker on desktop for the less-shady aggregate sites, accepting that the chapter list might not be perfectly organized.