I'd personally shoot for one that has USB-C for input and QC 3.0 for output. Thats going to cover the wide majority of devices and you won't be frustrated in the future having to pull out a micro cable to charge the pack when your future phones will all be C.

Depending on size and cost, there are a lot of options that would fulfill this.

On the big end, RavPower 20100mAh for $50: https://www.amazon.com/RAVPower-Portable-Qualcomm-20100mAh-Nintendo/dp/B019IFIJW8/ref=sr_1_3?ie=UTF8&qid=1518212831&sr=8-3&keywords=usb+c+battery+pack&dpID=31ROW8cIauL&preST=_SY300_QL70_&dpSrc=srch

RAVPower 20100mAh Portable Charger with QC 3.0

Wonder if this battery pack will work, if so could give you 5hrs

https://www.amazon.com/dp/B019IFIJW8

I got this one https://www.amazon.com/gp/aw/d/B019IFIJW8/ref=sxl1?ie=UTF8&qid=1468613110&sr=1&pi=AC_SX236_SY340_FMwebp_QL65

Quick charge and USB c so I can still use it with my next phone

Amazon tells me otherwise:

http://www.amazon.com/gp/aw/d/B019IFIJW8/ref=mp_s_a_1_1?qid=1464049009&sr=8-1&pi=SY200_QL40&keywords=quickcharge+3.0+battery+pack&dpPl=1&dpID=31xGOAIYq%2BL&ref=plSrch

I've had the QC 2.0 version of the Ravpower 20100mAh for the past year. It's been excellent. It got a a lot of use at a convention charging my Moto X as well as friend's Nexus 6P simultaneously. Very fast, and no problems. It's huge though, and somewhat expensive as a result.