I typically use whatever device, iPhone, iPad, iMac is closest. But there are times when one device is needed more than the other.
For instance, I need the computer to do Excel and organize a book. I need the mobile to read books and capture, augment, and publish content.
Eventually, everything will converge into hybrid tablet/laptop kind of like the Microsoft Surface minus the keyboard. In the future, all we’ll do is touch.
This is just the beginning of format shifting though. As wearable technology like the iWatch emerges you may prefer to use your watch for certain things over other devices.
“Whatever device is closest” is just a general tenet. Depending on what you need to accomplish, it’s actually more complicated than that.