Altaria

Altaria, the Humming Pokemon, is the showy performer of the Dragon family, not a fighter. Its Attack stat is weak and its Health is middling. This alone makes Dragonite a stronger option on defense than Altaria. 

That said, raising an Altaria isn't a terrible option, as it is set to be a fairly efficent Mega Evolution. While its DPS is absolutely nowhere near the levels of monsters like Mega Rayquaza, it can spread its mega boosts for an extremely long time, which can actually work out better full-team average DPS depending on what its team mates are.

Best PvE Offensive Moveset

• Dragon Breath is the superior fast move of choice for PvE offense.
• Peck isn't particularly strong, but can be chosen for a Flying-type role if stronger Pokemon aren't available. 
• Sky Attack synergizes well for a Flying-type role, and is also the strongest charge move in neutral fights. 
• Dragon Pulse makes Altaria a budget Dragon-type attacker if the player lacks stronger Pokemon. 
• Dazzling Gleam outperforms Moonblast, but both lack STAB. 
• Flamethrower is worthless on offense for Altaria.

Best PvE Defensive Moveset

• Peck is generally preferred on defense due to its higher base power than Dragon Breath. 
• Flamethrower has great counter-coverage for Altaria, making it a prime choice.
• Sky Attack has the shortest damage window, and deals moderate damage as a 2-bar move. 
• Dazzling Gleam lacks STAB but is less likely to be resisted by attackers. 
• Dragon Pulse is easily dodged, and also most likely to be resisted. 
• Moonblast as a 1-bar move might not have a chance to be used before Altaria faints. 

Dragon Breath and Peck are both excellent, providing incredible energy gains and decent damage; Dragon Breath is generally preferable for its shorter duration and helps widen Altaria's coverage.

Sky Attack isn't particularly amazing, but it is Altaria's cheapest attack and benefits from STAB. Flamethrower melts down Steel-type opponents who try to wall Altaria's Dragon and Flying damage. Dragon Pulse can be used for extra firepower against opposing Dragon-type Pokemon. Moonblast and Dazzling Gleam aren't particularly amazing, but they provide additional coverage against Dark-type Pokemon. Return provides nearly no relevant coverage.