This is an extract from the games database of all Pokémon, the natures listed next to them are the top 3 most common natures for that species, where the level is between 90 and 125, this is to filter the results in a way that better represents what people are training/using the most. 

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The most common natures are not always going to be the best choices, where the Pokémon's rarity is higher, the chance of more people having a beneficial nature is lower. 

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When it comes to pre-evolutions, for example, Bulbasaur and Ivysaur, the natures for Venusaur take priority, as it's expected this will be the end result. For Pokémon like Eevee, each evolution is its own ranking, as they vary greatly in their selection.