Sniper

At the very best, the Sniper is in essence a single rifle infantryman, armed with a gun and primitive camo wear. His attacks are fairly mediocre, but against infantrymen, officers, and machine guns, he is practically second to none, being capable of wiping them out with a single shot. Snipers are as slow as spies, but they are also stealthy units, too - they are also capable of seeing hidden units and have fairly high LOS, making them highly valuable not just for high-priority wet work, but for scouting and spotting whereso needed. Just keep them away from buildings and vehicles, and you will be fine.