Feeble reminder that Sketch is yet another graphics/drawing app pressed into UI design service rather than being specially built for that purpose. I use Antetype for high fidelity mockups: http://antetype.com/
Hope it's of some use to others.
All my colleagues use Sketch (I work at a service design agency and we do a lot of UX as well) so I've used it occasionally for compatibility. What I primarily miss in Antetype is artboards.
The auto layout feature in Antetype is more or less unique in design tools as far as I know, apart from the ones that produce actual html, and they suffer from their own problems.
The symbol handling has so far been superior in Antetype as well. It'll be interesting to try out the stuff that they've introduced in Sketch.
The reason I've been a Sketch user for all this time is that it was the closest thing to a UI design rather than photo manipulation / drawing app I could find.
Looking forward to seeing how Antetype holds up.