imo the best source is a locally hosted komga server. Download/purchase manga for hi res copies from places like AB/nyaa/baka/etc, rip scanlations with something like hakuneko or fmd2. Place in a folder, install komga+komf, point it at said folder. Komga scans in manga, komf scrapes metadata from manga updates or MAL. Use the Komga plugin in mihon and your progress is tracked both ways.

Much higher res most of the time, better translations, faster, more reliable, no ads, no tracking, no downtime unless your shit breaks, consistent across devices, and if you get tired of your library you can still just jump to the mangadex plugin or whatever I guess