My favorite is easily Gallade and in the new generations Hydreigon is shaping up to be one of my favorites but Gallade will always be my personal favorite. Such a beast. One of the highest attack stats, amazing moveset, and easy to counter weaknesses.
EDIT: Also Rattata is up there because the FEAR combo is AWESOME! If you don't know what FEAR is, it stands for Focus Endeavor Attack Rattata. It's a lv.1 Rattata with a moveset of Quick Attack and Endeavor and it has a Focus Sash equipped. Focus Sash allows the holding pokemon to retain 1 HP if it's health would otherwise be knocked down from 100% to 0%. Since Rattata will move second you use Endeavor which puts the opposing pokemon's HP equal to yours so it knocks the other pokemon's HP down to 1, and then since Quick Attack gets priority your Rattata attacks first and finishes off the opposing pokemon. It's really broken and really unfair but it's pretty funny lol. Basically the only counters are to switch in a ghost type pokemon or to use another priority move like Mach Punch or Extremespeed.
EDIT: Also Rattata is up there because the FEAR combo is AWESOME! If you don't know what FEAR is, it stands for Focus Endeavor Attack Rattata. It's a lv.1 Rattata with a moveset of Quick Attack and Endeavor and it has a Focus Sash equipped. Focus Sash allows the holding pokemon to retain 1 HP if it's health would otherwise be knocked down from 100% to 0%. Since Rattata will move second you use Endeavor which puts the opposing pokemon's HP equal to yours so it knocks the other pokemon's HP down to 1, and then since Quick Attack gets priority your Rattata attacks first and finishes off the opposing pokemon. It's really broken and really unfair but it's pretty funny lol. Basically the only counters are to switch in a ghost type pokemon or to use another priority move like Mach Punch or Extremespeed.
