This will depend on what you want to do. For gaming the Gear VR is best, for a basic headset I bought the Mattel View Master and I like it. No strap, no access to headphone port so you would want Bluetooth headphones, but it's a real nice sturdy head set. It also comes with a little augmented reality disk that's pretty neat.
You can get a View-Master for $25. Much higher quality than any Cardboard that is actually made out of cardboard. No head-strap though (although you might be able to mod one on).
Also the magnet works with the magnetometer (ie compass), not NFC. And Cardboard V2 doesn't use the magnet, instead it uses a lever to tap on the screen.
Oh, they're way ahead of you.