Since the theme is Invest, Fundamentally, which fundamental analysis is the best?

Honestly this depends, most of the answers listed here seem to indicate cash flow but while that's a decent snapshot of the current business, fundamental analysis may also include understanding the company's ability to generate this in the future. Buffet calls these "moats" and are discussed in depth in the Little Book That Builds Wealth by Pat dorsey. So understanding the importance of competitive advantage, debt and Return on Invested Capital are all sound levers to consider, but ultimately follow the approach that suits you best

The company cashflow, debt ratios and patterns will give you a feel of how the company is functioning. however, there are no best analysis since everyone is just analysing and guessing the direction of the company in the future.