I can't answer as it really depends on the source. If the options are ethically farmed and home-cooked, red meat wins. If the options are antibiotic-dopped and factory-farmed, I wouldn't touch any of it.
I would say beef right now because I havent ate it in a while. I'm not a huge fan of meat and get sick of the same thing all the time. I loved chicken but I eat it so much with my diet I can't stand it any more