Jillius is a pretty powerful fighter, even without much of his army. He can turn some into monsters with the use of a colored mist, as seen in Empire of Dreams, of what he did to Chipple, Muzika, and Dr. Medim. He does have some magic that can work well on Garlen's robots in a way. His army, while seemingly weaker than robots, might be a lot more plentiful, as Jillius still had his empire and army up and running after being defeated by Klonoa, while Garlen has been halted of his plans on creating an empire in a few occasions. (Ow, my throat
So with that being said, I'd say Jillius. Despite Garlen having a stronger army, and having generally better strength, Jillius' army might have the slight edge, without the need of taking some time repairing robots, possibly bigger numbers, and Jillius' strong magic powers, with being able to defend himself well, even without the use of machines, as Artsy has stated.