One of the most frequent questions at this moment is what Legendary Pokemon should we power up? What are the actual best Legendary Pokemon to level up and to use my Rare Candies or Stardust on?
Every person would power up Mewtwo first. Its DPS is overall better, and not that many Raid Bosses resist him.
The second choice would be Raikou. Its moves and stats are majestic. Raikou is a very strong DPSer in any situation and has excellent specialist uses, which are quite similar to Mewtwo. They’re both useful and powering them up is the best option.
The third choice of mine would be Moltres. This is because it has the best overall DPS, and is the 3rd most useful. Even though this yellow Legendary Bird is not as good as Mewtwo or Raikou as a gym battler, but as an overall DPSer is good in Raids. Lugia though is not that much of a use in the Raids because of the low DPS, the only exception being a possible anchor against some Pokemon like Focus Blast Mewtwo.
Lugia is a bright spot in the gyms, where the high Total Damage Output can be put to use despite its lower DPS. If you want a good big attacker, your best choice would be Lugia. It is the total opposite of Mewtwo. If you are that type of a player which does not mind if the Raid is taking a little longer and do not like switching attackers, you might get some use out of Lugia.
Articuno is the ultimate counter to Dragonite, but Dragonite is not a Raid Boss. I would recommend holding off the powering up for this Legendary until it does become crucial in fighting against Dragonite or Salamence.
Zapdos is an awesome Pokemon. This large bird with its spiky feathers is good against Solar Beam Ho-Oh, but unfortunately is worse than Raikou. If he gets a moves change, you might have to rethink him.
Entei is a nice Fire Type with an extraordinary Total Damage Output, but the DPS is worse than the one Flaeron has, even more miserable than Moltres’.
Suicune is totally useless. With the Hidden Power Rock, it will have a small hollow against Ho-Oh. The look of Suicune is quite nice but other than this, it is hopeless.
A lesson learned is that you should power up your Legendary right after the moment they stop being available. Nobody wants to throw Stardust and Rare Candy into powering up a 76% IV Mewtwo, only to catch an 85% the following days.
This analysis is made thanks to a Redditor called jake_eric and I would definitely follow his guidelines. Good luck and catch ’em all!