If you are deadset on creating a DRM for your game the most secure type is one that is consistently online checking the client. I should note that these kinds of DRMs are understandably very unpopular and I would not recommend them. I will however say that the purpose of DRM is not to completely stop piracy but instead to reduce the period from which it will be hacked and pirated so that you do not have a massive first day distribution problem where everyone got it free so that they do not buy it. But even then most players want to support independent developers and some pirates will even purchase your game later on anyways.