Whom should I ultraevolve?

Necrowing
Rexobone
Omegawarym

You’re posting on hunter island bruh. haha. I do not have any of those legends, but look up their movesets on the neo monsters wiki. Evo the one that has the most helpful movesets/passives. Rexo is usually a good option I hear for any scenario. 

http://neomonsters.wikia.com/wiki/Neo_Monsters_Wikia