It's tough to decide without seeing all the Pokémon, but I'm planning on Froakie, Helioptile, Flabebe, and Skrelp so far. If I had to pick from the currently revealed Pokémon, Amaura and Meowstic would round out the team. Malimar and Pyroar are Pokémon I'd consider rotating in though.
I tend to pick the water starter first, and the second stage convinced me that Froakie will be a pretty good choice. I also want to try a Fairy Type, but I don't like Dedenne, Spritzee, or Sylveon, so that narrows it down to Xerneas, Swirlix and Flabebe. I'm getting Y, so that just leaves Flabebe. I also really liked Skrelp from the moment it was revealed (although I originally was going to start with Fennekin so it wouldn't have been a redundant type). Helioptile could get dropped, but I tend to pick Electric over Grass for countering opposing water types. I want a Psychic Pokémon, and actually like both Meowstic and Malimar pretty well. I'll probably use the one you can catch sooner. My friend is picking Tyrunt, so I agreed to take Amaura, but I do like Ice Types a lot, I'm just worried it might be really slow and the two 4x weaknesses could cause it problems.
Sapphire Scramble Challenge completed.
Now taking Pearl Challenge Final Team:
Luminion Torterra Bastiodon Rapidash Carnivine Luxray