Best Mac for college: CS or engineering with Premed

About to be a senior in high school in August and i want to start saving up for a nice Macbook air or pro for college. I've never owned a mac, but have some experience from school and friends and after 3 windows laptops in the past 5 years, I've decided to get one for college. I'm planning on majoring in either computer science or petroleum engineering with Premed. How powerful of a laptop do i need for these majors, or college in general? I want to use this one laptop for all 4 years. I like the air because of the portability, but i watch a lot of movies so the retina display appeals to me. I feel like the 15in Rmbp with 2.0 ghz i7, 8gb memory, intel iris graphics would be the best choice at $1899 with education pricing and a $100 gift card. Should i go refurbished and save $200, because I feel uncomfortable spending this much money for something not "new". I'll be buying it next summer, but want to have an idea of exactly how much i need to save per month until then. Help??

Tldr; best mac for computer science or petroleum engineering (both with premed)? thanks.