Nearly equally.
I prefer reading books/comics on my iPad hands down. The Kindle app is nice on the MBA for searching through books, but reading on the iPad is far superior IMO. I always use my iPad in the morning as well for catching up on the news using apps like Flipboard, BBC, Zite, ESPN, a couple local news apps as well. And I'm more likely to use it to take notes in class. (it's the original reason I bought it). Oh and games.
However, with my MBA I do web browsing in my down time, YouTube/Vimeo are much better to view on it. Emails, Tumblr, and a few other social activities. Writing papers is easier due to it being easier to research on. Light and I mean very light photo editing. And downloading movies and the like. Then streaming stuff to my AppleTV.
I was tempted to get an iPad Mini, bought when I saw no retina display I instantly purchased an iPad 3 when Apple sold those discounted.