Need advice on mac for programmer/developer

In your question, you mention C# which implies a .Net and Windows platform to run side by side with OS X through bootcamp or a virtualization system. Windows is bloated and really takes up space (a Win 8 VM with VS 2012 is around 28gb) and you will really feel it if you go for the 128gb in the Air so I would go for 256.

With regards to the processing power, it depends on how bigs the apps are that you are writing. I have a 2011 Air and my iOS apps are great on that. For work, I have an Asus i7 running Windows with a top performing SSD and I can really feel it taking strain when running solutions with lots of projects, even a web app with a services layer takes it's toll when doing debugging. I have tried this on my Air in a bootcamp setup and gave up very quickly as the CPU really takes strain as is it is clocked so low to keep the voltage low and give the great battery life.

The extra cpu muscle of the rMBP makes sense and also the beautiful screen. I have good eyes and love high res screens to get as much on as possible. I also think that this will give you the best life span as well.

 

Just my two cents:
I'm a developer and find that the 15" screen is barely enough real estate for me. I purchased a 13" MBA ( I wanted something easier to carry around ) but moved back to my MBP because of the screen size.

 

1280x800 is too small. 1440x900 is alright, but you really want something larger if possible. 2 or 3 external monitors is preferred.

As far as space goes, unless you plan on using your laptop for college and chucking it, 128 is useless, and 256 is borderline. I have a 500gb hard drive, and only 71gb free on my work computer. If I wanted, I could free up about 40gigs by deleting personal music and games, but there's still about 400gb of "stuff". Virtual machines, windows, etc...

Keep in mind this is just for web development, not objective C or even graphic work.

 

Maybe you should try to find the old 17 inch MBP. That MB still has the most gorgeous screen to work on. 1920x1200 is a breeze, and even easier to the eyes than a new retina. And it is killer to open it on your desk/lap: you sure make an entrance!

 

Retina MacBook Pro. You get more pixels per inch so everything is sharper.