If you had to choose only one of the 3 financial statements to analyse, which one would it be?

The Cash Flow Statement, and more importantly, Operating cash flow (OCF). OCF is the lifeblood of a company and in my opinion, a more important metric of a company's financial health then net income. Although it can be done to some degree, cash flow is harder to manipulate under GAAP than net income.

I would most likely analyse the cash flow statements, since they measure the cash flow of the company which is fundamental to all kinds of operations for the company. Cashflow is helpful because at the end of the day, the business is all about earning cash, and runs on cashflow.

Cashflow statements also flow from the balance sheet and income statement, so you can actually see how cash is generated and spent on the different "income statement" activities, like revenue and expense, and the balance sheet items like PPE, debt, accounts payable etc.

Companies can often hide behind accounting policies and activities to mask earnings, such as depreciation, assets write down, valuation etc. However, cashflow statements measure cold hard cash, which is much more representative of how a company is doing.

The split of different cashflow activities is also quite useful for categorising the 3 different forms of major activities of a business, and compare them to each other.