There are really 3 different heads you need to be comparing. Not just 2.
PR3 - "B16" off all B16a motors and b17
PR3 - "Type R" off b18c5 or jdm type r b18c and b16b
P72 - "GSR" off b18c1 or jdm gsr b18c
Now stock, the PR3 "type r" > P72 "gsr" > PR3 "b16"
The type r has a stock port job which gives it better flow over the gsr/b16 heads. The gsr and b16 heads have similar flow (one might be stronger in one area where the other is stronger in another, but they are pretty close flow wise) but the gsr head has a smaller combustion chamber that boosts it's compression something like 0.2 points over the b16, which results in slightly more power.
The gsr and b16 heads also have slightly different injector port angles, marginal difference, but I don't think there has been any tests to show if either is more advantageous than the other, just pointing it out.