A lot depends on what you want to use the machine for, do you consider weight very important, updradability very important? For light use, not much difference other than weight. The MBP has a slightly faxter cpu but that will be overcome for some tasks by the faster response of the SSD vs hard drive. Both have the same graphics processor so that doesn't affect the choice.
You cannot upgrade the MBA memory after purchase so get as much as you will need. Also, the SSD is significantly smaller than the MBP hard drive so get as much storage as you can afford.
Both for light duty should be fine...just make sure if you go with the MBA you outfit it as fully as you can at the time of purchase.
It is very difficult to tell you buy this or that...what I would do is go to an Apple store or reseller, and spend some quality time with both machines and see how each performs. Does one seem to do the tasks you want better than the other? Does one seem quicker than the other? Then you have some data points to better inform your decision.