My main team consists of:
Blaziken
Xerneas
Delphox
Charizard
Lucario
and one HM slave.
I picked this particular team because half of them came with mega stones at a very early point in the game. Also if you haven't gotten a torchic through mystery gift then get it. Mega evolution is a very good thing to just have with you all the time. Also, before anyone says anything about me having 3 fire types in my team at a time, listen to this. They are not only fire type. Not only are all three fire type, but they are also fighting, psychic, and flying. It leaves room for a lot of strategies in the long run. If one isn't very effective against something then I can switch to something that is. I fought lysandre's mega gyrados with a Blaziken and won because it's a fighting type. Sure it was super-effective against me, but because of blazikens "speed boost" ability I already had super speed on my side. I used double kick and took it out before it could land a hit on me.