Since it's eastbound TATL flight, I would pick UA over LH due to better seat comfort and better bedding since you'll be sleeping most of the way. As noted above, LH seat is hard, uncomfortable, and risk of footsie. An added nitpick, the ergonomics of the shifting the IFE monitor and opening the massive center console just to get the tray table, makes the LH feel like a very poorly designed seat--maybe to get people to pay more for F.