Comixology is the leading service for selling digital comics. The selection of comics is vast and prices are ok. It has an online site and mobile apps. The applications contain decent readers. Nothing customizable like YACReader or Perfect Viewer but they work. I should note that there is a quite handy feature for reading comics by frame by frame on mobile devices.
Most of the comics are spoiled with DRM but the platform itself doesn’t force this. Some comics are offered without DRM too. They can be identified with a small download icon next to the age restriction box in the respective store page.
So far everything is pretty good. The one huge flaw in Comixology is that the service is ridiculously slow. It’s not uncommon to have to wait a full minute before a page loads. This is just absurd given that Comixology is owned by Amazon, one of the world’s leading cloud service providers.
A practical tip: Before buying a comic from Comixology, check what it cost in Amazon Kindle store. Oftentimes you can get it with a about dollar less from there (at least when conversion rates are applied). And if your accounts are linked, comics bought from Kindle will be transferred to Comixology too. Just note that the inverse isn’t true. Comics bought from Comixology won’t end up in your Kindle library.
All in all, Comixology gets it borderline done, which is just what to expect from a modern business. I’d love to see a real alternative. Sadly, they are few and small.