A:AnswerHonestly, the size. My brother and I have the same specs but he has the pro and I have the air. The air is lighter and easier for taking places in my opinion.
A:AnswerI wouldn't be using this for serious photo editing, if that's the case I would go with the macbook pro. If you're just learning photoshop and want to learn, you can use this but you will hit bottlenecks on the memory and the CPU speed. It could get laggy if you start getting more advanced.