This thread is going tonget moved to In-Game Team Help once Zeffy finds it, but while it's still here:
If you're going to get into competitive play, Fennekin is the way to go with your starter. All of the starter Pokemon have exponentially superior hidden abilities, and you get an opportunity to catch any of them, with their HA, at the end of the game, so the reason for choosing Fennekin is entirely separate from its own potential as a Pokemon: the game assigns one of the three legendary birds to your playthrough based on your starter, and if you picked Fennekin, you get to catch Zapdos, which has the most competitively viable typing of the trio.
Otherwise I'd pick Froakie, because Greninja has the best movepool of the Kalos starters.
Since you're looking into other Steel types, I'd recommend backpedaling to Route 6 and picking up a Honedge. Its final evolution stage, Aegislash, can pretty much plow through the final stages of the game, and it has significant natural bulk, unlike your Lucario. Just make sure that you keep its move King's Shield so that it can switch between blade and shield forme.
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