Choosing finance means selecting the most appropriate source for a business's situation. The claim that there is no single best source β that it always depends on the situation β is largely sound, but it is worth examining how far it holds.
The case that it always depends on the situation. The appropriateness of any source depends on several case-specific factors. The purpose and time period matter: a long-life factory needs long-term finance, while a temporary cash gap needs a short-term source β so the 'best' source for one need is wrong for another. The form of ownership matters: a sole trader cannot issue shares, so a source that is ideal for a plc is impossible for them. The level of existing debt matters: a heavily geared firm may be unable to borrow and must use equity, while a debt-free firm can choose a cheap loan. The owners' priorities matter: one owner prizes control (favouring loans), another prizes low risk (favouring equity). Because all these vary from firm to firm, no single source can be best for every business β strongly supporting the statement.
The case that some general rules still apply. Although the specific source varies, some principles hold almost universally. Matching the source to the purpose and time period is always wise β funding a long-life asset with an overdraft is dangerous for any firm. Retained earnings, where available, are almost always the cheapest source, so a profitable firm should usually consider them first. And for a given, well-defined situation, there often is a clearly most appropriate source β for a profitable, low-debt firm wanting to keep control and fund a long-term asset, a long-term loan is hard to beat. So while no source is universally best, within a specific situation a 'best' source can usually be identified.
Weighing it up (criterion). Whether the statement holds depends on the level at which 'best' is judged. Across all businesses, it is true that no single source is best, because purpose, form, debt and priorities vary so widely. Within a specific situation, however, the factors usually point clearly to one most-appropriate source β so 'it depends' does not mean 'anything goes'.
Judgement. I largely agree: there is no single best source of finance across all businesses, because appropriateness genuinely depends on purpose, time period, ownership form, existing debt and the owners' priorities. But the statement should not be read as meaning the choice is arbitrary β for any given situation, applying the matching principle and the choice factors usually identifies a clearly most-appropriate source. So the truth is that there is no universally best source, yet there is normally a best source for the situation β the skill is using the case to find it.