What characters do you regret spending skill shards on? With most new characters coming out being sharded worthy, i wish I didn't shard:
Blue allied soldier (helped out a lot as early player, quickly outgrew its usefulness)
Assassin artillery dog (never use, seemed good in pvp without really doing pvp at start)
Gunner Valkyrie (can't find out best use for her, still a work in progress with talismans)