According to the Huffington Post Shahien Hasiripour, it's Wall Street. Hands down.
The crux of Nasiripour article is this: Big corporations and big banks benefit from very low interest rates — and the actions and policies of those institutions prevent the benefit from being passed on to average Americans.
Nasiripour opens with the following point: Quantitative easing essentially allows large investment funds to buy securities ahead of Federal Reserve purchases — and then make money by selling those securities back to the US government at a premium. Nasiripour describes it as a classic front-running scheme:
"Over the coming months, the Fed will then communicate its specific plans well ahead of any such purchases, allowing wealthy investors and firms a chance to buy those assets first so they can sell it back to the Fed at a profit."
(Bill Gross at PIMCO isn't doing himself any favors with quotes like the following, from a Bloomberg Television interview: "…from mortgages, yes, in terms of buying them in front of the Fed and selling them to the Fed over the six- to 12-month period of time.")