When starting up, a bank may require a personal guaranty since your company doesn't yet have a credit history but, as a rule, a shareholder's liability is limited to the amount invested into the company. Creditors cannot reach beyond the assets of the company in normal circumstances. The same is true with lawsuits. However, you can avoid this with the use of a LLC or by electing to be treated as an S Corporation. Transfering ownership and raising capital are usually easier through the use of stock.
Corporations usually have a perpetual life as well, distinct from that of the shareholders.