Getting a good rope isn't the trick. Getting the biggest guy to be on your team - now that's the trick!
Choose a good, heavy rope.
Look for grade-A manila rope - that's what the pros use.
Stay away from nylon and polyester ropes, because they'll give people rope burn.
Pick a rope between 115 and 120 feet long for two teams of eight people.
The rope should be between 1 and 1 1/2 inch in diameter.
Look for manila safety line, which has a wire-rope core, if you can't find a rope of the right thickness. The line is used for climbing, search and rescue and construction.
Look for rope at sporting goods stores. Ropes specifically made for tug-of-war will be looped and braided at each end.
Try rock-climbing supply or marine shops if sporting goods stores don't have a rope.