If there's a specific champion that you're after in one of the crystals, then go for it. It would be totally worth it in that sense as the chance to get said champion is quite high (I pulled Warlock and Quake from there and BG's love story with Aegon finally came to an end). If you're more focused on 6*s then go for the shards. It's all down to what you're looking for.
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Taken the 6 star shards