Easy question even though there are a number of fun encounters. I play operations a lot on my level 50s and the one which stands out for me from the currently live ops is Operator IX in tfb.
The whole fight is fun, I like the environment design too, and for hard mode your group really has to be co-ordinated and everyone participates equally in the whole fight. It was also interesting working out the best way to set up the colour pairs for our particular group for HM so we could be most effective, a good puzzle.
The balance of this encounter is particularly good imo. I have level 50 toons for every occasion so have tried this as both melee and ranged dps, tank and healer . I find it an essentially equal experience on all, unlike some other encounters there is no advantage to ranged dps over melee, although the normal balance of 2 of each is still nice, and no one role has a harder or easier job than the others on this fight and that's great.
When patch 2.00 hits there are some good boss fight coming in scum and villainy but I've not counted them for now as they are only on pts. I'm encouraged by the progressive improvement in ops design in the game though.
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