Re: Air V Pro
Depending on what you mean by "complicated programs" the ULV CPU in the Macbook Air might give you some trouble. The Macbook Air uses what is called a "low voltage" CPU. Basically this CPU draws less power but as a result is much less powerful overall. This is fine if all you are doing is web browsing, office work, etc. but becomes an issue when you want to run more complicated programs. Now, a ULV CPU has the ability to "turbo clock" which basically means it ramps up its clock speed and functions as a non-ULV CPU...so basically if the computer needs to draw on that extra power to run something it can do it. This isn't as efficient as a regular CPU though and it is fairly power intensive, so you'll experience quick battery drain. If you are using CPU-intense apps frequently, you may get considerably more mileage out of the Macbook Pro.
As far as CPU upgrades go, I don't recommend the ULV i7 in the Macbook Air as it doesn't provide significant performance gains for the cost. The 2.6 Ghz i5 in the Macbook Pro is a decent upgrade that will help the MBP perform much better than the MBA. The 2.4 Ghz i5 that it ships with stock is fairly comparable in overall performance to the MBA CPUs so if you aren't planning to spend the extra money on the i5 upgrade for the MBP, you will get about the same performance overall, albeit with the battery life issue on the MBA (though the Macbook Pro has a much shorter battery life overall anyway so you're still losing that juice regardless).
For RAM, I highly recommend a minimum of 8 GB and, ideally if you go with the rMBP 16 GB. This is because the RAM in MacBooks is no longer user replaceable so what you get stock is what you have. RAM is the #1 area that you can upgrade for faster performance and the #1 thing you will want more of as your machine ages. 4 GB of RAM is acceptable in an Apple computer right now, especially for entry level tasks, but 8 GB is a ~significant~ upgrade in terms of speed, multiple apps being able to run, etc. You should consider purchasing as much storage space as your budget will allow for this reason as well, though IMO 128 GB of storage is adequate on a laptop and there are good external storage solutions. If the Macbook is your only computer though, you may want that extra storage space built into your system.
The rMBP has a much better screen and better graphics capabilities compared to the MBA with base features but other than that is fairly comparable in terms of overall performance so if you don't plan to spend to much on performance upgrades it really comes down to choosing between battery life and screen quality.