PH's or pro-hormones are not active steroids, they convert to active steroids in your body using enzymes you have in your liver. Oral steroids are just that, active in oral form. Most are methylated to survive the first pass through the liver.
In general, oral steroids are going to be stronger and more efficient. Oral steroids will have a greater impact on your HPTA (generally). Because of this, post cycle recovery is more of a priority with oral steroids. Both will take your lipids to the garbage.
Their aren't really a lot of true prohormones left. Some call them that when in reality they are oral steroids, just sold OTC. Soon, there won't be many of those left either. But hey, you can always get a doctors note to smoke as much weed as you want - coming to a state near you.