In light aircraft, non-instrument flight, apply (nearly) full aft elevator before beginning the takeoff roll or at some predetermined speed?
It's a matter of the conditions you are faced with.

The first instructor was teaching you soft/rough field technique, where the focus is getting as much weight off the nosewheel as soon as possible to minimize its rolling drag on a soft surface. Besides the drag on the nosewheel, the thrust line acting above the drag axis of the mains on soft ground tends to drive the nose down, so you need to compensate for that as well. The other thing is having the wings producing partial lift from the nose being high also helps reduce the effect of the soft ground.

You might also use this technique if the surface is firm but has a lot gravel, that can get sucked into the prop, and you want the prop as far away as possible while the airplane is moving slowly.  I'll start a run on firm surface with loose gravel with the nose held high but let it come down a bit as speed is gained and there is less tendency for the prop to pull rocks up into it.  

Thing is, you need the nosewheel for steering control until the rudder becomes effective, so you give up a lot of potential directional control with tail down technique early in the takeoff, so you only use it to the extent you need to.  Besides directional control, the nose in the air condition is very draggy and can delay acceleration, actually extending the takeoff run.

There are basically 3 procedures that I follow:


Soft/rough field - tail low all though the take off to keep weight off the nose wheel and as much weight off the mains as possible.  You may use flap in this case when you wouldn't ordinarily for the same reason.  You stay in ground effect to accelerate before climbing.
Firm but short field - tail low late in the takeoff and rotating early so the airplane gets to flying speed already at its takeoff pitch attitude. This is to have the airplane lift off at the earliest possible point and may include use of flaps that aren't normally used.  You stay in ground effect to accelerate before climbing.
Normal takeoff - elevator neutral or only slightly nose up, for best steering control and acceleration until rotation at the normal rotation speed.  


Students using different instructors always discover quite a bit of variation in techniques as instructors apply their personal preferences.  A perennial problem in the industry.