Gary Oak always seemed to have the upper hand against his rival Ash Ketchum in the Pokemon anime. However, Ash did eventually beat him, and that's probably because Gary didn't make all the right choices when it comes to the Pokemon he trained.
The trainer did have some impressive Pokemon, including the likes of Blastoise, Arcanine, and eventually Electivire. Unfortunately for him, some of his other Pocket Monsters let him down in crucial moments.
Note: This article reflects the personal opinion of the writer.
Top 3 Pokemon Gary shouldn't have trained in the anime
#3 - Nidoqueen
Gary's Nidoqueen is certainly the least impressive half of the pair completed by his Nidoking.
While the Pokemon was able to defeat Ash's Tauros during their match in the Silver Conference, it quickly let Gary down against his rival's Snorlax. Snorlax knocked Nidoqueen out easily with the move Ice Punch.
Gary would have been better off putting all his efforts into training Nidoking, rather than splitting time between it and his Nidoqueen.
#2 - Magmar
While there have been Magmars that have proven how strong the Pokemon can be in the anime, Gary Oak's is an exception.
Although the Fire-type had a crucial advantage against Ash's Bug/Fighting-type Heracross, it still managed to lose the battle against it during the Silver Conference.
Gary should have just worked on making his Arcanine an even more powerful and fiery force rather than wasting his time training Magmar.
#1 - Golem
Gary's Golem didn't make many appearances throughout the anime, and it's for a good reason. In fact, it likely shouldn't have ever appeared at all.
Like others on the list, Golem earned its spot here because of how it let down its trainer during one of his most important moments: a battle with his rival.
Ash's Charizard made easy work of defeating Gary's Rock/Ground-type Pokemon. In the end, it was Charizard's Dragon Rage that knocked Golem out. The trainer should have chosen a different Rock-type to focus his time on.