I started with the Bhagvad Gita, because I was familiar with the mythology around the events of the Mahabharata, so it seemed like a more accessible way of beginning. I'm currently working through a translation of the Puranas. There's obvious differences between Gurmat and the Vedantic strand of philosophy, the promotion of the caste system being the most glaring one, but I try to understand why such beliefs originated, and then appreciate why Gurmat disavows such teachings.
That is why sometime adults are like spoiled kids and even kids are bit of mature nowadays. A person with wrong mind and negativity will always find faults and negative in everything that happens around him. Bad part is that other lives will be effected by this immaturity.