A Pokemon Go Trainer who goes by the name of jake_eric on Reddit has made a great guide of all Gen 1, Gen 2 and Gen 3 Legendaries worth to power up. So with his guidance, we now have the ideal guide that will unquestionably come out usable when you are in a difficulty which Legendary Pokemon is the best to power up and why.
The first on the list is Mewtwo, simply because this Legendary Pokemon is the best generalist at the moment. The new Gen 3 might outperform Mewtwo, but he will be still at the top. The Psychic/Focus Blast Mewtwo is quite unique, and it gives it a special edge. Shadow Ball Mewtwo is good too. Against Tyranitar or Gengar, which are Mewtwo’s best counter, he is a top pick. This power of Mewtwo is unmatchable.
Kyogre is the second choice. This Pokemon has the highest CP in the game. With its Waterfall/Hydro Pump, it is a great counter against Regirock and it is also good in gyms. With the Dragon/Ice moveset, Kyogre becomes a great counter to Regirock, better than Articuno. This moveset makes this Pokemon the best Ice Type without actual Ice typing. With its worst charge move, it is a good counter to itself and also good enough rival to Zapdos.
Raikou is third on the list, consisting out of amazingly good stats and moves. He will be a quite important counter to Kyogre. He is also an extremely good counter to all the Legendary Birds. As far as a generalist, Electric is great, and by far the best Electric Type in the game. Its DPS is good enough to be in a battle against a Pokemon he is not Super Effective against. The Pokemon that come after Raikouonn our list, are not that good.
Latios is something special because of its Dragon Breath/Dragon Claw moveset. Unlike Latias, Latios has the stats to back this moveset up. It is nice to use Breath and Claw. The Psychic and Dragon Latios are great generalists, and Latios will become one of the best gym-clearers.
Rayquaza is next on our list. He is stronger than Latios and maybe than Raikou. He is fifth on our list only because it looks like this Pokemon is a better Dragonite. If you have a maxed Dragonite, it isn’t worth it to waste Rare Candies on Rayquaza. Even with the Flying moveset, Dragon Tail/ Hurricane Dragonite is still a better choice. But if you decide to power it up anyway, it is a great pick into almost every battle, only if he is not going against Ice, Fairy or Rock.
Groudon is currently in a battle with Kyogre for the highest CP. He is sixth on the list only because his type is not that useful and every Ground move sucks. This is the reason why Groudon is recommended to have Solar Beam instead of Earthquake. Nobody needs Ground unless Raikou comes back. But after all, Groudon could be useful against Regirock and Registeel, but not as good as Kyogre or Moltres/Entei.
Moltres and Entei are seventh and eighth. They are very similar and their performance is quite similar. The preferred one is Moltres because he has a higher DPS and performs better against Grass, Bug, Ground and Fighting moves. Entei, on the other hand, performs better against Ice. The last time these Legendaries were ranked, Moltres was above Entei. But now with the weather boost, Entei is worth using in gyms.
When Kyogre gets released in the game, Articuno will lose its charm. But Articuno is a good Groudon counter. When Mamoswine comes to the game, Articuno will become irrelevant.
Zapdos is at number ten. This is only because Raikou is straight better than him. Raikou is better in every field than Zapdos. Zapdos though has resistances that might be useful, such as resistance to Grass Type. If he could only learn ThunderShock, he would be more relevant and could overtake Raikou in DPS.
The players who want survivability could easily pick Lugia. The players who pick DPS hate Lugia. This Legendary is one of those Pokemon that works well for some people and not others. This Pokemon has good moves and can last a really long time, which means that it has an extraordinary Total Damage Output. When powered enough, it can be useful in Machamp solos. For the ones who love speed in raids, we do not suggest to use Lugia.
Ho-Oh is next. He got totally ruined by the moveset. It is not the best Fire Type, nor the best Flying type. It has great stats, but the absurd moveset ruins everything. Even though it has horrible moveset, Ho-Oh has a very high CP. When this Legendary Bird finds its place in the game, it can be extraordinary.
Regirock is quite strange. He has a double-Rock moveset, but we are quite unsure where to put him. He is probably a worse Golem. His stats are strictly on the defense side, and funny enough, he is not allowed to defend a gym. His stats are not that bad but just put in the wrong place. After this Pokemon, the rest of the Legendaries are not that useful, so we will put a few words for each.
Latias is a bad version of Latios. They both have same stats, but Latias is on the defense side. Not recommending to power this one up.
Regice is outclassed by many Pokemon. Its stats are worse than the other Regis, and Metagross is simply better than this one.
Suicune was called a worse Vaporeon, but now it has a new name: worse Gyarados.
We do not have anything to say about Mew, Celebi, and Jirachi because they are irrelevant. They do not do anything that special.
Deoxys has stats of 1/1/1 on Game Master. Our guess is that he will not be released until these stats change. And since he is in progress, we will not speak about him yet.
You now have a great guide on what Legendary Pokemon from Gen 1, Gen 2 and Gen 3 to power up, thanks to jake_eric and we hope that this post will make it easier for everyone.