Hmmm... personally Im not a fan of the airs, so Id say the gor with the pro. BUT, if you have the patience, Id say wait for september/october (whenever the next apple event is) because it is likely they will add the haswells and possibly other upgrades into to pros.
What would I buy? The air all day long. What should you buy? Who knows, you didn't mention what you'd use it for. Do you want extended battery life, extra portability, and the latest processor? Or do you want a bigger (slower) HDD, a faster (older) processor, and an overall heavier machine with less battery life?
I would absolutely go for the air. It feels like a generational change over the old pro (which I expect to be phased out in the next update). Battery life, hard drive speed and portability are in a different (much better) class.
To the OP, I currently own the MBP 13" that you mentioned and am extremely content with it. I think you should weight in if you truly need a optical drive built-in, ethernet or firewire 800 and the ability to later upgrade the RAM & storage yourself and a very competent mid-range processor ?
For me all of the above were a resounding yes since I am have a sizable collection of DVDs bought over the years and whenever I need to troubleshoot my home internet connection I have to plug it in via Wi-Fi. Add to the fact that I am consume all my entertainment content via my laptop & the usefulness of having a audio line in/out that's analog/digital means I can plug in a Toslink cable and export my DVDs & iTunes videos through my old home theater system. I checked out that they MBA don't have that except for the headphones use.
But the new Haswell powered MBA are no pushover when it comes to battery life. That alone might had tip the balance in it's favor but I can manage with a 6+ hour battery life since I like to leave my laptop plug in most of the time. Your call...
128GB is way too small for me so given those 2, I'd definitely go with the MBP but I'd replace the HD with an SSD. If you bumped up that Air to the 256GB version, it would be a closer call but I'd still probably go with the MBP because I really want the option of 16GB RAM. I also really like having the extra ports and the option for 2, internal HDs. Those things greatly outweigh the Air's portability and new processor for me. I also don't really care about battery life. However, that's just me. Your needs might not match mine.
Still though, the new MBAs are really impressive machines.