Whatever clicks with the way you are wired to think and gets you results. My first glimmer of personal development was David Hawkins and a Course in Miracles, Gary Renard's book, and more enlightenment focused books, but I found I preferred a more science minded approach which hacks the human brain and explains why we act the way we do by analyzing the brain structures and human evolution, which I found with Leo and a few other sources. I don't necessarily believe in spiritual enlightenment aside from it simply being a state of mind you can achieve with the right inputs (or lack of inputs as the case might be) I've found the book "your survival instinct is killing you" to be quite informative, but really Leo's work is more than adequate for my goals. He took all the best content and did a lot of the sifting through it for me, which is why I did throw 50 bucks his way in a donation and got the nice little picture that I saved kittens from a cauldron of boiling acid
Even with these books, videos, gurus, etc, without the discipline to get rid of the hedonism in your life and set goals designed to rewire your subconscious mind with better habits, all the knowledge in the world will be useless because intellectual knowledge doesn't translate into a better state of being unless you apply it in a way the limbic system can understand, which is actions and experiences. If I watch one of Leo's videos and then get stoned and play video games, not much progress is achieved versus watching his video and going and lifting weights or having a more productive hobby that gets me out of the house.
I'm not the type to worship any guru as some sort of "special" figure anyways.. people are people and nobody is really more "special" than anyone else. They might be more advanced spiritually, but if they are they'd be the first to agree with me on this point.