accountability and regulation:
What level of transparency and regulation is appropriate for the business?
What is the size and nature of the business and what major impact does this have on any decision?
How much resource (your own or that of staff) can you allocate to complying with all the legal formalities associated with different structures? For example, making all filings with Companies House.
How important is it to access finance (loans (debt funding), share sales (equity funding)). Funders (banks, venture capitalists, and the public markets) will require transparency before funding. The minimum requirement is usually three years checked financial statements, but they may want more.