Lucario has always been revered as a master in offensive versatility, due to his massive coverage, excellent Attack and Special Attack Stats, and superb boosting options in both Swords Dance and Nasty Plot. Adding on to his great power, the Aura Pokémon possesses new found feats in moves such as Rampage, Giga Spark, Magnum Punch, Diamond Blast, Magnet Force, Psygatling, Raze Earth, and even Wood Hammer. With all of this coverage, Lucario is able to hit every single Pokémon in the Tohoak Region for supereffective damage. (Except for Sableye & Sableater, of course.)
The only real downside is that the only way to obtain Riolu is through an in-game trade at Shamouti Island at the top floor of the Department Store, by trading away a Larvitar. (Best to hack Riolu early on, if you really want to use him.) Also, Lucario has meager bulk and rather average Speed at 90.
Aside from that, Lucario is easily one of the best Pokémon to utilize in Vega and he should always be considered when you are in need of an offensive powerhouse for your team.