Which MacBook Pro configuration is best suitable for Iphone/Ipad App development?
Unless you're planning on working with an external monitor I'd always go at least with 15" Pro or the 13" Air. Both are fine machines for coding iPhone apps. Working in Xcode on an 13" Pro (1280x800) is doable, but rather unpleasant. 

If it'll be your only machine I would recommend the 15" MBP, as you might need Photoshop (or similar) for UI design. At that point you would notice the weaker CPU and graphics in the Air or 13" MBP.