The failure of any business has ripple effects on suppliers, employees, distributors and customers. If the business is General Motorssuch effects are larger. But since GM is many times larger than most companies, the subsidy needed to keep going is correspondingly larger. There is no reason to think that the ripple effects are larger, relative to the size of GM, than the consequences of the failure of a smaller business relative to its size.
So the return on the taxpayers' dollar is not likely to be larger if their largesse goes to a big company. Indeed, since the large company has readier access to a range of alternative funding options, a need for government support is more likely the result of deep-seated competitive weakness than temporary shortage of funds which can so easily cripple a smaller business.
That is true of the carmakers, whose problems are of much longer standing than the current downturn. In automobiles as in many industries, economies of scale are technological, the diseconomies of scale human. Human factors in business are generally more influential than technological ones in determining the long run fate of a company.