If DC and Marvel are your thing, then all you need is Comixology, and maybe Marvel Unlimited (if you think you'll get value out of it). With Comixology you'll buy books via their webstore, then the books appear in your digital library which you access with the Comixology app.
Anything else is piracy - while cbz/cbr readers have their legitimate uses (and there are lots of good ones), you don't need them to read purchased DC and Marvel books.