Back when Tigers used to smoke.
The Battle Frontier easily. I thought the graphics in Gen 3 were good but nothing mind-blowing compared to some other JRPGs I saw. That was until I got to the Battle Frontier and man did it blew my mind on what GameFreak could do with the limited GBA hardware, castes, pyramids, temples, dojos. The Battle Frontier not only stood out as a strong post-game, it had a great awesome look to it. All the more disappointing we didn't see it's 3D counterpart in the remakes.