I read a bunch but nothing clicked until The Secret of the Vajra World and The Crystal and the Way of Light. After that everything made sense. Before that it was like wearing sunglasses, glossing over "big" words and intellectual phrases with self contempt ( ie, I'm way too dumb to study Buddhism).
Now that I think of it, it was Bhagavan Das' book It's Here Now. Are You? that propelled me to delve into the dharma. Reading his experiences of Kalu Rinpoche, the 16th Karmapa, Dudjom Rinpoche, Dilgo Khyentse etc inspired me to take refuge.