Free-flowing heads, in order:
#7120 (1991-1995 OBD-I)
#0630 (1996-1999/2000, OBD-II w/o COP/DIS ignition)
Third place is a tie - the #0331 (COP/DIS OBD-II, 2000/2001-2007) flows better on the intake side of things, but is restricted on the exhaust. The #2686 (1987-1990) flows better on the exhaust, but has restricted intake due to lower ports and a sharper turn into the cylinder.
Also note that the exhaust ports on the #0331 head are smaller (meaning you'll have some trouble using the later header on the earlier head,) so you may want to just use an aftermarket header or an OEM that fits the earlier head. The 1999 intake should swap without too much trouble, fitting up to the aftermarket header or the earlier OEM unit.
I'm still trying to collect heads so I can flow one cylinder from each on the same bench to get a better benchmark (relative flow from one head to the other, I/E bias, ... and some porting experiments) but I've not yet gotten all of the heads I need.