Most of the people who have an iPad and an MBP have at least a 15". It helps get rid of some of the redundancy. The iPad screen is 9.7", the 13" MBP's screen is 13". Not a huge difference. If you must get a MBP, go for the base 15", provided that you have the money to pay for it. If you don''t have the money for the 15", I wouldn't recommend getting a MBP at all.