Fletchling.
This question is obvious to any competitive player. Talonflame is probably the cheapest and most ridiculous Pokemon in the game right now (besides Mega Pinsir). This is because of Gale Wings, Talonflame's ability, which gives +1 priority to all Flying type moves. For a Pokemon with such a bad typing and a low Attack stat, this ability is a godsend.
Talonflame @ nothing
Ability: Gale Wings
EVs: 252 Atk / 252 Spd / 4 HP
Jolly Nature
- Acrobatics
- Flare Blitz
- Swords Dance
- Roost / Taunt
It is as simple as setting up Swords Dance and repeatedly using Acrobatics. If there are Steel types, Flare Blitz them. The Flying + Fire combo goes unresisted against everything but Rock, which means if you can get them out, Talonflame will be free to 2HKO or OHKO the rest of the opponent's team (unless there is Heatran or Rotom-Wash, which you should also take down before attempting to sweep with Talonflame). Roost allows you to heal off Flare Blitz recoil, and Taunt ruins a bunch of walls who would otherwise give Talonflame some problems. It can also protect you from getting paralysed or poisoned by Toxic or Thunder Wave.
If Talonflame doesn't suit you, Staraptor comes next thanks to its impressive Attack, great Ability, and almost flawless coverage with its STABs + Close Combat.