OV-chipkaart is actually a joint venture between NS, Connexxion, GVB, HTM and RET (all various public transport operators). The system I like is the London Oys

OV-chipkaart is actually a joint venture between NS, Connexxion, GVB, HTM and RET (all various public transport operators). The system I like is the London Oyster-derived one, which New York MTA is now also using. It has the advantage of supporting contactless and NFC payments out of the box.