One of the big complaints about electronic media is the lack of support of library systems. Because libraries lend at no cost and an electronic copy is the same as an original copy, many media (whether music, video or print) have been reluctant to give lending rights. One of the few players in the electronic library world is OverDrive. Over the past year they have really expanded their software to allow for much more and much better access. I reviewed the iPhone app last year.
I thought the iPhone software was ok, but I was using it on an iPad and there was not native iPad app. Since that original review an iPad app was released. In addition, you can now check out ebooks, not just audiobooks. So the iPad can be a fairly basic reader that allows library checkout of books. The iPad reader is basic, but usable.
For audiobooks, I really prefer using my phone because it is the device that I am more likely to have with me all the time. So when I bought an android phone a couple months ago I found that Overdrive had an android app. Primarily, I am interested in the audiobook functions. The android app also allows for ebook reading, but I already have a kindle account and do not really need ebook library functions (I have literally hundreds of unread books on my kindle account).