If I am flying a determination Oicunn would the old or new damage deck be better? What's the main differences? Does anyone prefer the old deck?

I think it's an auto-include in your case.
There's a lot of "crit-deliverers", for lack of a better term. Even Whisper is once again considered a heavy-hitter in the meta.

I was just thinking the other day I wanted to revisit RAC-plus-ace, with Determination as RAC's EPT. Pair him with Vessery or "Quickdraw". -- Haha, off to the Squad List subforum.

Here are the differences: http://xwing-miniatures.wikia.com/wiki/Critical_Hit_Cards

The really vicious customer is Injured Pilot, which Determination ignores, but that's only one one ship protected from it. Both have the exact same number of Pilot: cards, so I don't see why Determination would be any sort of deciding factor for your choice.