Corporations shouldn't get taxed at all. All taxation should occur with the people that make up and own the corporation. All directly taxing corporations does is create a complex mess of double taxation that enriches accountants, lawyers, and politicians, and allow such people to hide and manipulate the very loopholes that get whined about.
Consider the famous Google tax evasion by funneling most of their income through Ireland. That's only possible because "Google's income" is getting taxed, and Google is a multinational corp that can shift funds around. The individual shareholders and employees have far less ability to shift income globally, and most certainly it's impossible for most of them to live in Ireland.
The irony is that the left typically rejects the idea of corporate personhood, yet demands higher taxing of corporate persons.