For the longest time, my favorite was Umbreon. I just loved his design and he's easily my favorite Eeveelution. However, with Gen 6, a new king took the crown...
...Fennekin. This guy is just too cute! Imo, he has to be the cutest starter we've ever had. I usually don't go for the Fire starter, but Fennekin won me over. He is also a complete monster in-game, being able to beat 7 of the 8 Kalos gyms! Crazy! Fennekin also broke the 3 generation long tradition of the Fire / Fighting starters and evolves instead into a Fire / Psychic type. About damn time, GameFreak. Overall, Fennekin is just a really cute creature and he's easily one of my favorite Gen 6 Pokemon.