I would not keep any of these. MBr IMHO is a step back. Yes, the screen is better, but the keyboard change is questionable, and the switch to USB-c is just idiotic. It was like spitting in Steve's face and telling him that his idea of mag-safe connector was sh*t. I like mag safe a lot and it did save couple of my MBA's from being
Mag safe on the MBA is flawed as the wire is at right angle to the connector meant the wire gets damaged easily. That's on the 2010 model don't know about other years. You're right about usb-c being the macbook's Achilles heel. If Apple added 2 full size sub ports and a hdmi port then it would appeal to a broader scope of punters.