Gtx 960m is equivalent to desktop Gtx 750ti. Gtx 970m is a powerful and better graphics card. G-sync has its own perks. If you are into playing competitive multiplayer games, then you should choose Gtx 960m with G sync. If you are into playing single player games or you play multiplayer games just for fun, then you should choose Gtx 970m without the G sync.
Btw, which two laptops are you considering right now? I am guessing that you live in India. You can let me know your budget in INR so I can help you better.