It's obviously difficult making a team as only a portion of the pokédex has been revealed so far. If I had to put a team together just based on what we know it would be as follows:
1. Froakie's final evolution - Froakie is my favourite starter ever and its final evolution is currently the only certain member of my team.
2. Mega Mawile - I want to use a Fairy type and a Steel type in my team (not to mention a mega) and this covers all and it looks really great!
3. Talonflame - I need a flyer and so far this seems like the one I would be using but is definitely switchable if a better looking flyer is revealed.
4. Malamar - I love Inkay so this seems like a certainty, plus its typing is great!
5. Gogoat - It's awesome and fills in my grass type need.
6. Tyrantrum - Dragon/Rock awesome
The only certainty is Froakie and I'm sure that my team will change drastically once I play the game.