I'm looking to purchase an external Hard drive. Something under 125$. I was looking into the WD Edge 500GB 3.0 USB 60$. Is there a huge difference between thunderbolt connection and USB downloads? If so, what kind of External HDD will you recommend for me with thunderbolt connection under 125$? I just want a hard drive that backs up my Mac. I don't want anything less than 500GB. Thanks!