Since armor is easier to get, you should always go for shards (needed for next card upgrade), but then you will still have plenty of enregy to farm items, since you can only attend to Hard dungeons 3 times a day.
i think going for shards from the regular campaign is a waste of time at the moment, since drop rate is rather abysmal. I personally, focus on starring-up 4 "easy to get shards" characters: Luminara, Boba Fett, Luke (cantina shards are much better drop rate) and Darth Sidious...spend regular energy on gearing up.... so far it works out well - i'm at level 44 able to finish most Galactic Wars and end up in 150-200 PvP bracket...
Shards then items. Just pick 2-3 characters to promote asap. Mine is Chewbacca via Cantina as I need him to tank harder for the 5th campaign, boba fett from cantina shipment also to tank dark 5 campaign and Luminara from galatic war as I can let go of consular with her. Arena shipment still working on sideous 65/80 ugh
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But seeing as you can only do hard missions 3 times a day, you should do those first and then farm gear.