I dont know for this one. I just like lucario

Well Slaking is a normal type Pokemon,while Lucario is a steel/fighting pokemon,which puts Slaking at a disadvantage,because of Lucario being a part fighting type,so if Lucario knows fighting moves I think it would be rather easy,and not only that,Slaking loafs around every other turn,which gives the Lucario more of a chance to weaken/attack it.

Slaking+Hammer Arm=Super Effective 1hit-KO

Slaking isn't always a Pokemon that attacks, that would give it quite as disadvantage, so I think Licario.