The Photo app on iPhone can do great job on photo editing if you shot your photo with iPhone.
If you really want to use different app, then use VSCO.
Spend more time shooting new photos, not editing the old ones.
Shot with NOMO CAM FR2. 
Shot with NOMO CAM FR2. 
Shot with NOMO CAM FR2. 
Shot with NOMO CAM FR2. 
Shot with NOMO CAM FR2. 
Shot with NOMO CAM FR2.
LOVE YOURSELF
CHARLIE YANG