Debating on which one to get for development

Depends whether portability or a little more power is more important to you. Personally I am in a similar situation to you and I am considering the 13" middle spec with 16gb RAM

 

I'm looking at the lower 15" MBP with Touch Bar. I could see that being helpful with debugging, the quad-core seems to be worth it when it comes to compiling large projects.

 

I went with a 15" screen for development. I find with debugging, code, and UI windows I needed as much screen real estate as possible.

 

I've gone for a 13" one with an adapter so I can use my Thunderbolt Display. Only went with 8GB RAM as that was all that the budget would allow, in an ideal world I would've picked 16 but 8 should be fine for 90% of the time. My current 2011 MBP only has 8 and it copes with most of my Xcode projects fine so I hope it'll suffice.

 

Ditto here... I just never have enough screen real estate with development... especially with all those Xcode panels. I particularly like Retina screens because I can drop the resolution when space isn't as tight to make things bigger without any noticeable fuzziness. I had stayed away from the 15-inches until now because of size, but the new one doesn't seem much bigger than my 13" Air (and is actually thinner).

Honestly I would think a dual-core would be enough, but obviously you can't get that at 15".

 

I've been doing iOS and Mac development on a 13" rMBP for a year and a half now; I just ordered a 15" version of the new rMBP. The extra resolution will be very helpful, and I'm looking forward to having a dedicated GPU so I can play a few games on the side.