I conducted a half-assed poll about a year ago on another forum. Of all the 18-XX lenses, the 300 was considered to be the worst. Of course that's an almost 17X zoom, quite a bit even for a superzoom. The 18-105 and 18-135 were both considered very good, the 200 adequate.
Take that for what it's worth. I like to search out sample photos from everyman and ignore you tubers when I want to see the true capability.
I haven't used that lens, but as Tim said, the 18-135 is a great all-rounder. I remember reviews said the zoom on the 18-300 wasn't very smooth, or was it just that it wasn't linear?... please report back when you get to try it!