At first I tracked the manga I liked with Baka-updates and downloaded them either from the scanlator sites or from mangatraders and read them offline. I still download from time to time, mostly from madokami or the scanlator sites. When I started reading online I mostly used Mangafox, which was tolerable at the time, and more rarely other readers like Otakuworks (now extinct) and the Mangatraders online reader for the short time it functioned. Then came Batoto and I started reading most of my manga there, whatever I couldn't find on Batoto I read either on the scanlator sites or on Mangafox although the latter was becoming increasingly annoying with all the ads. When the announcement of Batoto's demise came out I was devastated because by then Mangafox had become pretty much impossible to use and most of the other existing readers seemed just as crappy. So when Mangadex got started I was on board immediately and so far I wasn't disappointed. These days I read mostly here, the only other reader I'm using is Mangago which isn't completely ad-free and is less mobile-friendly but at least doesn't have porn or malware. I mostly use it to read series that aren't hosted on Mangadex. I also read on scanlators' sites or download on occasion but that's not very often.