Which 15" for learning to code?

Dedicated graphics is the biggie there.
..but also you get a faster CPU and double the SSD space.
...If you take the cheaper model ($1999) and add the cpu and ssd found in the $2499 model, it comes out to $2399.

..so for $100 it makes sense to just get the dGPU.

 

For coding you need a keyboard and a display. The CPU/SSD/GPU are completely insignificant. Battery life is nice but the rest of the hardware does not matter. The whole twice as fast SSD is nothing but a placebo anyway. You just cannot notice the difference in real use.
Get the cheapest and you will never no the difference.
dGPUs only matter for the 3d gaming in the off time. The difference between the CPUs are insignificant.
SSD space is needed for a home music/picture/movie collection but you will not need much space for the web dev work.

Everything said holds true for years to come. The difference between a notebook from now and 3 years ago might be big. The difference between todays low end and high end just does not matter, it isn't big enough.

 

The base 15" will be more than enough... Coding can be done on a netbook processor so I don't think you'll have an issue with power or staying relevant for a couple years.

What you'll probably want is a quality external monitor and a good keyboard. Screen estate is the most important thing for productivity.

 

For your purposes, even the 12" MacBook wold be an overkill. Why not get a 13" rMBP? Its more mobile and still has much more power than you would ever require for web development.

 

For web design, any 15" config will be more than adequate.

 

13" with external would be an excellent choice. You could even go 4k and break even with the 15".

 

Used 13" MacBook Air + external display. Cost = ~$1000

(I know this doesn't answer your question, sorry)

 

You don't need a Mac to learn programming. Development tools are widely available for WIndows, Linux, BSD, Solaris, and many other operating systems. It doesn't take much computing power either, so you're not stuck having to buy the latest and fastest hardware.

If you want the 15", it will certainly be great for your uses. I would get the cheapest one though.