[mengto]

I'd say there is zero learning curve. So much easier to get started for anyone new. My favorite thing about Sketch is the ability to use Pages and Artboards + Symbols for multiple screens design. That's the way I prototype nowadays; focusing on interactions and flows rather than static single screens and branding/image editing.

[justjimmy]

I can't imagine anyone using PS to do flows.

I actually use Illustrator to handle the different artboards and do my flows and wireframes.

My team member uses Sketch for precision coordinates - our developers have Sketch too so they can just load it up and get coordinates for each slice.