I am a professional blogger and I had reviewed many power banks myself.
I would like to suggest you some best power banks for your need
As you are gamer you will need a power bank which can be charged while you are using it to charge your phone too.
This is called pass through charging almost all new power banks has this technology
Here are some :
1 Anker power core
4 Xiaomi 20000 mah
Alway try to compare your mobiles battery and power bank capacity which would help you to select appropriate power bank
Here is source and detailed review www.powerbanktalk.com/best-portable-power-bank-review-2015