I honestly think that the Icebreaker is the most functional exotic to have in PvE Endgame content even if it isn't actually equipped more often than Gjallarhorn, because people use it to refill some of their Special ammo conveniently.
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Icebreaker for sure. My load out on all 3 characters is Fatebringer, Ice Breaker, Corrective Measure. I switch them out situationally though.