Breloom versus Chesnaught!
Breloom and Chesnaught both have practical uses and have the potential to be important members on teams in high tiers. Breloom has long been a popular Pokémon, but Chesnaught is new on the scene. Which Pokémon is right for your team?
Chesnaught and Breloom share Grass-Fighting-typing, meaning that they would stack against many Pokémon with the same odds... Or would they? Both Pokémon share weaknesses to Fire, Ice, Poison, Psychic, and Fairy-type Pokémon, and a double weakness to Flying-types. They also share resistances to Water, Electric, Grass, Ground, and Dark-type Pokémon. Most moves would have the same effectiveness against Breloom and Chesnaught, although Chesnaught is bulkier in all defensive stats, meaning that attacks with the same effectiveness would take a higher percentage of Breloom's HP than Chesnaught's. If you are choosing Breloom or Chesnaught to resist a certain type, e.g. Water, Chesnaught would be the best choice. If you are choosing Breloom or Chesnaught for coverage over a certain type, Breloom is the best choice.
Breloom's Attack stat is considerably higher than Chesnaught's at 130 versus 107, packing more power behind its attacks. 130 is one of the highest base Attack stats in the game, making Breloom a very powerful attacker, especially behind Swords Dance.
Chesnaught has higher Special Attack than Breloom at 74 versus 60, giving Chesnaught more potential as a mixed attacker. However, mixed attacking is not recommended for Breloom or Chesnaught, as their Attack stats are much higher than Special Attack and their movepools compliment Attack much better than Special Attack. Breloom is a more powerful physical sweeper than Chesnaught, and a better choice for an attacker.
Chesnaught's HP beats Breloom's out at 88 versus 60; neither Pokémon has exceptionally large HP. However, Chesnaught makes up for it with an impressive base 122 Defense and a decent base 75 Special Defense, making it a good choice for a physical tank and decent resistance to special attacks. Breloom has a fair base Defense of 80 and a mediocre Sp. Def stat of 60, endangering it especially to supereffective special attacks. Chesnaught makes a much better wall than Breloom, with a movepool that compliments its heavy Defense.
Breloom has a fair pool of powerful and accurate physical moves, such as Sky Uppercut, Seed Bomb, and Stone Edge, as well as Swords Dance to double its huge Attack, making Breloom a very dangerous sweeper. Breloom is also notable for its access to status-inducing moves such as Spore, Stun Spore, Poison Powder, and Toxic. Spore is especially useful as the only extremely accurate way to put the opponent to sleep, giving Breloom time to Swords Dance while the opponent sleeps or switches out. Breloom can also use Leech Seed, but this is not recommended because it tends to sweep opponents out quickly.
Chesnaught enjoys a large pool of hugely powerful moves like Hammer Arm, Wood Hammer, and Stone Edge. Chesnaught also has access to defensive moves such as Spiky Shield, Leech Seed, and Synthesis. If you enjoy accurate status-inducing moves such as Spore, Breloom is the way to go. If you prefer a defensive twist, you should choose Chesnaught.
Breloom's Ability is exceptionally important in considering its moveset, because its Hidden Ability, Technician, increases the power of moves with a base power of 60 or below by 50%! This makes options such as Mach Punch, Force Palm, Bullet Seed, and Power-Up Punch viable. Breloom also has access to the ability Poison Heal, which causes poisoning to restore its HP. If you let Breloom hold a Toxic Orb, severe poisoning will be automatically inflicted at the end of the first turn of the batte (unless Breloom acquires a different status in the first turn). Severe poisoning will increase the amount of HP recovered at the end of each turn. If Breloom loses its item, it will not lose its status of severe poisoning. If Breloom carries this Ability and runs Façade in its set, it can do 140 damage while poisoned! Breloom has a third Ability, Effect Spore, has a high chance of inducing a status on the opponent when Breloom is hit by a physical Attack. Breloom has some pretty cool Abilities up its sleeve!
Chesnaught carries Overgrow as its standard Ability, boosting the power of Grass-type moves by 50% when Chesnaught has 30% or less of its maximum HP. Its Hidden Ability, Bulletproof, prevents use of bomb-like or bullet-like moves against Chesnaught. See the Database's page on the Ability Bulletproof for details on the moves affected by this Ability at http://pokemondb.net/ability/bulletproof. Breloom and Chesnaught both have access to abilities from both the offensive and defensive sides of the spectrum, so choose a Pokémon based on whichever Ability you think would be most useful on your team.
I hope this answer helps!