TOP:
JG:
MID:
SUPP:
ADC: 
Honestly with this comp you have so much lockdown capability, tankiness, dmg, heals..all around solid comp imo. also depends on enemy team
Garen gives good tanking in general, also his ult is a heavy hitter.
Amumu is an awesome engage, he can rope in and ulti, also he's good peel with his Q..
Ahri is good for poking, and peeling with her E, as well as out playing with her R, shes a heavy hitter mage
Sona is a jack of all trades support, she has the poke with her Q, Heals with her W, Move speed buffs with her E, and a stun (I think?) with her R.
Jhin is one of the hardest hitting ADCs i know of aside from vayne of course..but his stun ability with slowed enemies makes him valuable, as well as his ability to be engaged in a teamfight at a safe distance with his R. He can use his E for gank detection, and his Q for general poking and waveclear.
In a team fight Amumu will initiate with his Q+R. Garen will followup and Q their CC mage, wreak havok with his E, then finish off the ADC with his R.
Ahri will stay by the ADC and poke with her Q and W. and if anyone tries to get to the ADC she can simply R behind them, and E to peel them off the adc and continue damaging. Sona will be inbetween Garen/mumu and ahri healing and poking, ulting the enemy frontline.
This is my ideal team comp :)