Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I'm an academic and prefer the larger iPad because I find it more comfortable for reading pdfs. That's a subjective issue, though, you might feel otherwise. While the iPad mini is smaller, the iPad Air isn't exactly so heavy that you won't be able to carry it around.
 
I'd say the iPad Air would be better. I had an iPad 2 and 3 and I loved the size of the display. It was perfect since they were portable devices, but the screen was large enough to comfortably read web pages and PDF's on. When I was between buying laptop a year ago, I exclusively used my iPad 3 as my portable computer and I didn't have a problem. When I bought the first gen mini last year I thought it would enjoy the smaller size but I found that I barely used it. I just got an iPad Air and I'm loving the bigger screen again, and now that it's a lot lighter it's a lot easier and more enjoyable to use. If you're carrying a backpack, the larger footprint shouldn't be a size.
 
By the time you (theoretically) get an iPad model with the appropriate storage and accessories, and applications to serve as a laptop replacement, you might as well just get a 13" MBA. It will have a lot more functionality with a much faster processor, more RAM for actual multi-tasking, and OSX which let's face it people is 1000x better than iOS7 when it comes to productivity.

I think some people just want an iPad and try to justify truly "needing" it and trying to make it work as a replacement for a laptop.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.