IMO - The best of the new Gen VI'ers based on battling ability...
Greninja (with the Protean ability) (also the most fun of the starters)
Goodra (great Attack & Sp Atk - but very weak on D)
Noivern (Dragon's are always good as long you don't meet ice)(Noivern has incredible speed)
Hawlucha (great speed and attaack)
Aegislash (Powewrful -with Stance Guard/No Guard - but slow)
Also rans: Gogoat, Clawitzer, Tyrantum, Aurorus & Charizard (with Charizardite X).
All the Megas are fun but I wish they changed type like Charizard X and Mewtwo X do.
Field Move Dispersal - no preference
Cut - Pangaroo, Hawlucha
Rock Smash - Gogoat, Pangaroo
Strength - Gogoat, Pangaroo, Hawlucha
Surf - Gogoat, Pangaroo
Fly - Hawlucha
By the time you need Waterfall, you'll have other options
I don't remember Flash being used anywhere
And welcome back to wasting your precious time on pocket monsters.