MacBook Pro 13 inch for work
If your programing needs include displaying an iPad with retina simulator, then perhaps a 13" MBP limited real estate will slow you down. Choose a 13" MBP for mobility.

From my talks to programmers who are happy with only MBP 13" (without external display) are programming HTML, Terminal/console shell scripter types. The others who develop apps for iOS tend to either have an MBP 15" or MBP 13" with an external display.