Hughes 500. Indeed In the era of Sycamore, Whirlwind, Hiller, H300 B47etc,the horizon attitude for each airspeed was the generally agreed instructional technique. However with the advent of the 206, R22, R44 the design requirement was for a level cabin over most of the cruise speed range. This meant that the the teaching had to change to "select an accelerative/decelerative attitude with reference to the horizon position in the windscreen, overcome the flap back with the cyclic and approaching the desired airspeed, reselect the attitude back to where it was and note the new cyclic position".
There is a design requirement now I believe for a positive pitch trim gradient with change of airspeed and indeed this is often achieved artificially via the AFCS as this is easier than the probably more tedious business of trying to achieve it aerodynamically. I seem to remember first experiencing this in the S76A.