Which one should I go for? Touch bar or non touch bar?
Well, as others say, the 12" MacBook should do the job - you don't need a supercomputer to at least get started on iOS development - so its really a case of deciding what you want to spend.
However,
- It doesn't have a particularly fast processor (I'm thinking particularly about running the iOS emulator for debugging)
- Development is much nicer with plenty of screen space...
- Can only run a single external display (you don't
need 3 displays for development, but try separate screens for "product", "code" and "documentation" & you won't want to go back).
- very limited connectivity (1x USB-C, not thunderbolt) - even if you use USB-C peripherals or buy new cables, you'll need a multiport dongle as soon as you want to plug in your iOS device for debugging while charging and/or connecting to an external display.
So I'd only consider the 12" if the super-portability was very important to you. Its not like the 13" is big and heavy...
The 13" non-touchbar has a more substantial processor and GPU, can drive a couple of external displays, has a bigger screen (duh!) and doesn't cost a lot more.
Downside - connectivity is better than the 12" - at least you can plug in your charger and iPhone at the same time - but with only two ports that have to do
everything, even with USB-C peripherals/new cables you're probably going to be dependent on multiport dongles or hubs.
Well the touch bar may very well be very good for Xcode in the future
...well, the touchbar isn't the only difference: the processor is slightly faster, the GPU slightly better and the connectivity considerably better (I'm having a day off from whining about USB-C/TB3 adapters, but 4 holes to plug stuff into is better than 2, which is better than 1).
Downside is (because of the processor) the battery life may not be so good... Oh, and the price.