What Navy DDS 2010 just said is true.
I'll give ya a quick reader's digest at a glance view between the two.
If you
1) Have a family
2) Have in-state or very low-cost dental education
3) Have past military experience, or plan to make the military a career
then the HSCP is the better plan between the two
If you have out of state or private school tuition rates then the HPSP is a no-brainer.