I used Sublime for a couple years before switching to Atom. As a disclaimer, I just do HTML/CSS/JavaScript so I'm rarely working with massive files. That's where I hear most complaints. However, I have yet to come across a problem with Atom that really gets my goat. There are occasional flukes - that is to say it feels like a fairly-early-on open-source piece of software - but nothing that prevents me from using it in a professional capacity.