All Pokemon that can evolve are better at using Eviolite than their evolved forms. More notable uses are Chansey, Dusclops, Porygon2, Doublade, and Corsola-G.
All (non-banned) base forms are better in LC than their evolved forms. All (non-banned) Pokemon that can still evolve are better in NFE than their evolved forms.
All Pokemon that can evolve are better than their evolved forms if the evolved forms are banned from a tier, and the pre-evolved Pokemon is not.
Charizard is better as a special attacker than Mega Charizard X.
Pidgeot + a boosting item (Life Orb, Choice Band...) is a better physical attacker than Mega Pidgeot. (Thanks SSuperiority!)
Any FEAR employer is better than their evolved forms for that specific use only.
Hope I helped! If any others come to mind, I'll add them. Please tell me any I'm missing.