The recent introduction of softhead lures has caused resurgence in the debate over whether marlin shy away from hard resin lure heads. The theory that softheads have a more natural feel is nothing more than a marketing ploy.
It is ridiculous to think that a fish can tell the difference between a hard and soft lure that is traveling at 6 to 8 knots and is armed with oversized stainless steel hooks. In reality the only reason a fish is going to shy away is when it gets pricked by the hooks!
The most important factor to consider is how the lure will track. Different style head shapes will make the lure act differently. For example a concave lure will track straight, while a slant faced lure will shudder from side to side and splash more.
Neither seems to be more effective than the other and as a general rule I like to run a combination of the two head styles.