You can try checking https://ayumilove.net/raid-shadow-legends-list-of-champions-by-ranking/, it should give general info which champions are worth to keep.

From rares, Kael, Apothecary, Spirithost, Warmaiden are good to keep. Coldheart from void shards, if you manage to pull it, but that is probably not going to happen very soon.

High Khatun from daily login rewards is great, other epics not so much.