Which accounting method is best? Cash based accounting or accrual based accounting? Does it depend on the nature of business?

The best base is the accrual. This is because it applies the matching role of accounting.

Accural method

Accrual method is universally accepted accounting method, because as Mr. Mostafa said based on matching principle i.e. income accrued but not received or expenses accrued but not paid.

But it can be viewed differently and more accurately once converted into cash basis.