I wish Crunchyroll had a better selection of manga. They have some good stuff on there, and I do use it, but they're lacking so so much. I know Viz gets most of the stuff I'd want to read, though, if anyone does, so I am stuck with them. Except if I'm paying that much, I'd rather just get physical copies. Bleh.
My main technical issue with CR manga is that both the web and mobile clients suck unwiped ass for letting me know which series I've favorited have a new chapter. There should be an icon on the favorites screen notifying me of unread chapters. That's it. That'd fix my main issue.. Of course, the website doesn't have such a screen, but it should.
The other issue, less main than the prior issue, is: it doesn't keep track of my progress on the webapp (which is mostly okay, since I very rarely use that, but sometimes I have to*).
(I haven't used it for a couple months now. If someone tells me they've addressed these issues I will be very happy.)
*Every now and then the mobile client just adamantly refuses to load a chapter. I've had this happen multiple times in a single binge-reading session as I'm lying in bed at night, and I either have to get up and read it on my computer or just give up.