Anyone should do the job.
However, when writing software, the larger the screen the better, as often times you have multiple windows open for different aspects of your development project (code, debugging, simulator, documentation, UI builder, etc...).
Of course if most of your development time will be done at a desk were you can setup an external monitor (an inexpensive 24" 1080p), then again any laptop would do. The asumetion being that you want the portability of the laptop so you can travel or surf the web while relaxing in a comfy chair (not actually working on your code).
Whatever you get, just get lots of RAM and sufficient disk space for your needs. Also make sure you have regular backups, as loosing a coding project is extremely painful, and the code you write to replace it never seems to live up to what you lost (first hand experience talking here). Also using a source code control system is useful. Checkin your changes on a regular basis, as sometimes coding changes do not work out the way you expected, and being able to go back to an older version is extremely helpful (also first hand experience).