Until you sign an agency agreement, there's no commitment.
Note that neither of these agents' off-the-cuff estimates have any bearing on what a buyer is willing to pay, and if you tell Agent A to list for Agent B's price, they have to do that.
Ultimately, people make these decisions based on trust. An agent has a fiduciary duty to act in your best interests at all times. Hire the one you believe will actually do that. The good ones aren't going to move much on commission, other than friends/family deals, because there's demand for their services, and the REALTOR(R) subculture inculcates a belief that it's a betrayal of the profession. But yes, commission is 100% negotiable, and you're free to haggle.
I'm an agent myself, btw... mostly so I wouldn't have to go through one when buying investment property. :)