MBA - larger screen, faster CPU, more RAM, runs desktop apps
iPad - Cell phone capability, portability
I really suspect that the decision is not as difficult as it seems for most people. I believe that most people who walk into an Apple Store (or Best Buy or whatever) intend to buy a tablet or a laptop and that very few actually switch from one to the other. Of course, many people will have both, but for any given purchase, I just don't see that many people who have trouble deciding.
What the f*ck are you talking about?
CPU and RAM? Who cares about that sh*t? iOS is so well coded that an iPad 4 runs circles around any computer on the market today, unless you need Computer-only tasks, making this 1vs1 stupid. Larger screen? Who cares about it when the iPad has "the" screen?
Who cares about desktops apps when you have apps designed just for your iPad? What about battery life?
Unless you need a trully fast laptop for some use (think the best of them all, a rMBP 15) the iPad is the best computer on the market today.