The bottom line is one who bashes the MBA based on the MBP being only 1.5 lbs heavier and only one inch thicker HAS NEVER USED AN MBA.
One has to truly use the MBA around the house, office, and traveling to understand just how big of an advantage the lightweight and thinness of the MBA is over an MBP.
I can understand people saying, "My MBP's only 50% heavier. That's only 1.5 lbs in a bag." But those people have never used an MBA in those conditions to understand just how big of an advantage it is.
Unless someone truly needs an MBP, the MBA is a far greater complete user experience in my opinion. I understand people seeing an MBA at the store and thinking the difference is minor. But when you get used to an MBA, it's really difficult to go back to a brick of a Mac like the MBP.
While the difference is only less than an inch in width and 1.5 lbs, it's huge in end user experience... night and day. I have had to move from an MBA to 13" uMB for a few months after my rev B MBA was stolen, and it was completely and totally the biggest disappointment I can ever recall when changing computers. The 13" MBP feels like a brick compared to the MBA. And one can fit the MBA into the narrowest of spaces in a tote. The differences are magnified far greater than anyone could realize until dealing with the transition from complete use of the MBA to 13" uMBP.
I really think that the average person who switches to the MBA with HDD will ultimately be disappointed. The differences in speed capabilities are dramatic versus a 13" MB/MBP. However, with the SSD the MBA becomes faster for normal tasks than the MBP with even a 7200 rpm HDD. This is not to say that ALL will be disappointed with MBA with HDD, because certainly some see the tradeoff as worthy for thin lightweight computing. My whole point is there is very little tradeoff to get the thin/lightweight experience when one goes with SSD in the MBA. For me, I recommend the average user should go with MBP if cannot afford the SSD MBA. For some using the MBA as a secondary computer may accept speed of HDD. For $300, and an added boost to CPU, the SSD is an absolute MUST for the MBA for anyone who wants to truly use it like a primary Mac or like a Mac in general.
At the same time, I recommend the MBP to those who truly need the extra capabilities, those who cannot afford the MBA with SSD, and those who don't know yet what they need (like the OP). And probably those who will be forced to use the same MBA for five years should consider the MBP for upgrade capabilities.