Keeping a neutral spine is better to deliver force into the bar. This is because it transfers the power better without losing a percentage of it through flex or excessive arch/curve.
The comments I get most by looking downwards or forward are:
- Better stability and ability to feel the weights between the midfoot to the heels.
- They feel their hips and glutes working harder (I personally got up with major butt sores)
- Looking in the ground gives them more confidence
- The quads feel more fired up
- Easier to keep the knees locked in place
- Easier to get the right positions while going down and less mistakes when shooting up.
The concept of packing the neck seems to come up more often these days.
Try and see what works best for you.