Fletching line -> As the "Com-Mon" Bird introduced in this generation, it became one of the most useful birds to ever exist, especially in Competitive play where Talonflame is such a common thing now and i can't blame the players. Priority Brave bird and access to moves such as Bulk up, Roost, and even Flare Blitz made it such a beast.
Froakie- Frogadier- Greninja -> Undoubtedly the "best" starter to be introduced in the pokemon world. Even without its HA, Greninja is awesome because its such as fast water type and has access to a lot of great moves. With its HA Protein, it becomes a real terror against teams.
Tyrantum - I love T-rexes and when this was introduced, I couldn't wait to get my hands on it.
Aegislash - One of the coolest looking pokemon this generation introduced, as well as a unique typing and playstyle. This thing is a true test of how a trainer can make such effective and epic predictions. Also, its a set of ghostly weaponry. How could I not like that.