The first time I just run through the whole game when I only had Pokémon X and don't remember well what I had with me except Greninja, Flygon and Florges.
On the second run I went with Delphox because though it is pretty useless Fennekin is still my favorite starter. I also had Blastoise, Salamence, Abomasnow, Gardevoir and Bibarel as HM-slave.
On the Y-version that I got after Christmas I ditched my starter which was Chespin and went with Gourgeist (absolutely brilliant in metagame as I just sweeped every battle with it), Blastoise, Hydreigon, Medicham, Ninjask and for some reason I don't remember the last one anymore. Sorry. :D
Anyhow, I recommend to try out Gourgeist as I just fell in love with it. Drawing a picture of my Y-trainer Lena with her Ghost-type Pokémon atm.