I think I would choose The early to mid Middle Ages. The wide variety of well made melee weapons and the high availability of chain mail armor would make slightly easier to survive close up encounters. Another reason, it'd be... well... FUN. I'm not just taking survivability into account.
I would like to draw a parallel between those times and modern day third world living conditions seen by the poor in India and Indonesia. These places saw the advent of 'bird flu' and 'swine flu'.
Look to these countries for your source of infection ;|
just flinging them around with the gravity gun lol. throw them into walls, trash cans, into on coming zombies, lol... ya way to much time on my hands...
during WWII, because of all the military ordnance that can be found.
During the old west, wide open landscapes, and smaller towns further west, not to mention there would be less lovers and more fighters during these times.
or now, advance means of transportation, and pretty much everything else besides all the modern US weapons and their tight fitting parts...old era guns for the victory!