I've worked for large companies (> 50,000) and small companies (<10). And I've audited (on a recurring basis) dozens of companies, gaining some significant insight into how good it would be to work at many of them. I didn't see any significant pattern whatsoever. There are large companies that are great to work for, and large companies that are terrible to work for. There are small companies that are great to work for, and small companies that are terrible to work for. Even within a company, where in the company you work, what job you do (and how important your work is to the company) have far more impact on how enjoyable working would be.
So basically, I don't care how big or small the company is... what matters to me is whether my work is viewed as critical to the company's success.