Here's my team; I use all of them competitively:

Malamar, holding a Life Orb
Ability: Contrary
Psycho Cut
Night Slash
Trick Room

Aggron, holding an Aggronite
Abilities: Rock Head, Filter (Mega)
Iron Tail
Thunder Wave

Scizor, holding a Scizorite (I'll either use this or Aggron, never both in one battle)
Abilities: Swarm, Technician (Mega)
Bullet Punch
Vacuum Wave
Swords Dance

Aegislash, holding a Full Incense
Ability: Stance Change
King's Shield
Swords Dance
Iron Head
Shadow Sneak

Darkrai, holding a Focus sash
Ability: Bad Dreams
Dark Pulse
Dark Void
Nasty Plot
Focus Blast

I've only lost about three battles out of 39 while using this team so I think they work well, but if there's a strategy I should use or a different way to use each Pokemon, let me know