More or less, the numbers are pretty close together. You can see mode details in each respectively links

https://www.youtube.com/watch?v=Pl4B...ature=youtu.be
GB was only used for initial burst, disabled for rest of the fight.

https://www.youtube.com/watch?v=-_C1...ature=youtu.be
GB remained the entire fight.

https://www.youtube.com/watch?v=wAus...ature=youtu.be
GB was hardcasted every 90 seconds (to align with cooldowns)

Looking at numbers for face value, it looks like GB has the highest damage output. Though I also included some numbers on each indivudal skill breakdown as well as damage source, and what I came up with was

-Proc rates across all 3 tests were very close together (variance of 1-2 clean/slug shots across all three tests)
-Test 1 (no GB) had less crits over the course of the entire fight, including auto attacks when compared to test 3 (hardcasting GB)

This was all on a stationary fight, so of course it'd be completely different on actual fights. As of the two Ex primals we have, it's definitely better to be able to hardcast into GB when there are downtimes, unload gauss round and ricochet, then disable it. It would be on a fight-by-fight basis so cooldown stacking would also change.