As far as what helps your vert most, that depends. Some people need limit strength development, and squats/DL will benefit them most. Some people need quickness/reactive strength, and things like plyometrics and OL's will benefit them most.
But regarding full versus parallel, definitely go full squats. I used to do parallel all the time. I switched permanently to full squats, and had the humbling reduction in amount of weight I could lift versus parallel squats.
After only a month of doing full squats, I had noticable improvements in my VMO development. Also, when I played basketball for the first time after starting full squats, I had very noticable increases in feeling of power and explosivenesss when jumping.
I also probably gained 2 inches in my jumping ability, as I could previously only dunk with one hand, but after that month I was finally able to dunk with two hands. The full squats seemed to give me just enough height to get that two handed dunk.
Granted, these weren't vert testing numbers, these were dynamic jumps on a basketball court, but it was very measurable to me in terms of how much height I was able to add relative to a basketball rim.