What do you need? Do you already have Nick Fury awakened?Some of them benefit a lot from the awakening and/or sig up, but it depends on what utility you need.For max sig you're looking at Angela, Void, or Valkyrie for biggest benefit - Angela counters all auto-block, Valkyrie counters all unstoppable, and Void counters evade and regeneration.Corvus being awakened gives him the glaive immunity, while Kitty being awakened means she takes no damage while phased which is a crucial part of her kit and Warlock can start degenerating the opponent when power burning/draining them.Spider-Ham is a great champ but doesn't REALLY need to be awakened.
For max sig you're looking at Angela, Void, or Valkyrie for biggest benefit - Angela counters all auto-block, Valkyrie counters all unstoppable, and Void counters evade and regeneration.
As PantherusNZ says: For max sig you're looking at Angela, Void, or Valkyrie for biggest benefit - Angela counters all auto-block, Valkyrie counters all unstoppable, and Void counters evade and regeneration. Conversely, if you want the biggest benefit at low Sig (and keep 199 Sig stones for a rainy day), then Kitty, Corvus and Warlock get most of the benefit of their Sig abilities at Sig 1.
Depending on your progression, Void is a very, very nice champ to have. Counters a lot of very tough fights and his damage delivery is so different that it allows you to play around a lot of funky nodes. Valkyrie would be my second choice for similar reasons.