I am surprised no one has posted a reply to your situation yet. I have seldom seen a TV Fool chart with the major stations in almost exactly 180 degree separation. It seems that something bi-directional would be ideal, if you have line of sight to the two transmitter locations from your proposed antenna location. I would be very tempted to try a simple UHF loop and VHF dipole (rabbit ears) perpendicular to the transmitters. The dipoles should only be extended about 28 inches, tip to tip. You could make something yourself or the Radio Shack 15-1874 indoor antenna is often recommended as it is proportioned more accurately than other indoor antennas.