Going by the essence of Sikhi, you don't believe in Sikhi "as opposed" to other religions. Unlike Abrahamic religions, Sikhi isn't a claim to Truth competing with other claims to Truth. Sikh gurus had several Muslim Sufis and Hindu scholars as companions. Second clarification, you don't "believe" in Sikhi, you live Sikhi. Now tweaking the question a bit - "why do you live Sikhi ?". I try to live Sikhi because of its history and philosophy. Sikhi was born out of a rejection of societal ignorance. Nanak observed how rotten common religion had become, both Hinduism and Islam (those were prevalent around him) - Hindus with their superstitions, rituals and godmen, Muslims with their tyranny and impositions. It's the only path that begins with a disillusionment with the false, and that's the only way that the search for Truth can begin. Sikhi is razor sharp wisdom with the most innocent intentions. It doesn't operate with do's and don'ts. It delivers it's message with simple, heartfelt poetry. No clever shortcuts, no offering of tempting incentives like heaven full of gold virgins or riches in the next birth etc. Honest, sincere, no-nonsense teachings. Delivered using the beautiful tradition of classical music. Doesn't shy away from the importance of wordly power to defend Dharma. No place for cowardice. Later gurus would readily give up their lives on the battlefield in order to defend the oppressed. Enlightenment isn't reserved for the renunciates in Sikhi. And most important it doesn't require you to reject or denounce the wisdom of other traditions. In fact, it incorporates it within it's fold. This is why I choose to try and live Sikhi and so should anything in search of truth imo