I've tried a couple but always come back to Comicbooklover.
Bought a license a couple of years ago and I haven't found a better reader, nor do I need one actually.
It does cost $25 or €18 but I do feel it's certainly worth the price.
Strange it isn't on the App store yet.
You can find it here
It's also available on the iTunes app store for both iPod/iPhone and iPad.
Both those versions are free and work like a charm.
For a free alternative you can always give FFView a go.
It's pretty barebones though.