I want to invest in buying books for one of these readers but I'd rather pick one and stick with it rather than use both. What's the verdict on these? For you folks that read on your iPhone a lot which has features you can't live without? Also can you read books from your iBooks on your Mac like you can with the kindle for Mac app? I've seen so many comparisons between the kindle and iPad but I'm looking for comparisons between the iPhone apps.