I'll give you the nod that the 32nd ID may have indeed served more continuous days of combat action as a division unit in the PTO than 1 Mar Div.
1 Mar Div: Guadalcanal : Aug 7, 1942 - December 9th, 1942 continuous.
New Britain: Dec 26, 1943- March 11th, 1944 continuous
Peleliu - Ngesebus: 15 September 1944 - 30 October, 1944, continuous
Okinawa: April 1, 1945 - 22 June, 1945, continuous
Total number of days engaged in combat action: Guadalcanal: 124 days ; New Britain: 75 days ; Peleliu- Ngesebus: 45 days; Okinawa: 83 days : total of 327 days of continuous combat action as a division unit.
no Marine would ever consider individual decorations for valor as a measure of the "better" in a comparison of combat units.
The OP and question posed specifically dis-enfranchised any formation below division size, IMO - so although MANY of them exist that deserve a place in the top 10 for combat units during the war ( I do agree with you on that) , I would not add them to my own list of Top 5 divisions to serve in the war.
As I noted before (in post #9):
General factors for "best" include (IMO)
Loss ratios to enemy casualties inflicted.
Number of days in combat conditions
Areas in combat - enemy forces engaged.
Opinions of battlefield superiors (Corps and Army commanders - who did they turn to as their "go to" guys?)
These four areas denote which units were not only the most effective in engaging enemy units, but which units were recognized at the time by their own contemporary commanders as being among the most effective at achieving the mission and disabling the enemy through combat engagements.
As with anything - YMMV