If we use PNG - for iOS we will use @x1 @x2 @x3 size per image (which is just a click a way in zeplin/sketch). Android - around 5 image sizes, meaning we have to maintain 8 PNG images per graphic element.
while SVG - will work for iOS and android but there are technical limitations. For example, the SVGs are getting distorted when being rendered. Though we might be able to fix it by looking deeper on each elements/layers of the SVG through Sketch.
I hope someone can help us to decide the best format to use for our app.