The nature of UG's is really subjective and that is personality-dependent. While IM may have assigned a room, including an UG, it takes work to reassign a room and it takes even more work to find the room you as a customer really want. Not just category, but view, bed size, proximity to ice maker & elevator and so on.

My gut says the lounge because the agent likely has more time to help you, but it may be the agent at the FD if that person happens to have time and is willing to spend it on you.