Pokemon GO Battle League is an excellent way to obtain a good amount of Stardust, berries, Candy and maybe earn an encounter with a Pokemon that you will most definitely like. Through these battles, you can also evaluate which Pokemon is best for your Power-team during Raid Battles.
The Trainer Battle is a system that contains three different leagues, with different requirements such as max CP of your Pokemon. As you know, the GO Battle Leagues are in a constant periodical rotation. The only thing is that you have to have a win after win to continue getting bigger and better rewards.
As the Leagues progress, you will see every Pokemon going from Pokemon with high CP to Legendary Pokemon. Many players tend to favor other Pokemon over these Legendary beasts, as they have lower CP than the regular Pokemon that can perform better.
A post on Reddit has appeared, in which the user u/MikeClaus has listed every Pokemon with perfect IVs that could be useful in the highest League, which is the Ultra League, so we have decided to post it here, and the list will be from the highest CP to lowest.
If anyone has another suggestion, you can place your comment on the Reddit post.