An interesting alternative possibility is the US XF5U "flying pancake." The original Zimmerman prototype proved to be a good flying machine on very limited horsepower. The production model was expected to hit 500+ mph (probably a highly optimistic figure) but even if it only did a bit over 400 it would still have made a powerful alternative to helicopters. The aircraft could take off using a very short run of just tens of yards and land nearly vertically.
A variant for use as a small transport with landing gear suited to rough fields might have been a viable alternative to the helicopter. Certainly, the higher flight speed, ability to fly over a larger range of altitiudes, the probability that it could actually defend itself against an enemy aircraft, and its longer range all argue that it would have made a good helicopter replacement.

Vought V-173 / XF5U-1 Flying Flapjack Info