If you compare the screenshots attached, that focus mainly on the UI chrome of Balsamiq and that of Sketch, you’ll notice minor but significant differences in the relative bulk of each app’s UI chrome.
Especially when working on smaller displays (the attached are screen caps from my 13 inch MacBook Pro) I find it much easier to handle the more svelte UI of Sketch which gives me more workspace. I like working in Balsamiq too- but only when I am connected to my external 24" monitor.
The Balsamiq inspector pane is just that much wider than Sketch’s to irk me on my 13" screen.
Hoping there might be a more slender UI chrome for Balsamiq in future releases!