I've switched back and forth between RawTherapee and darktable for a few years now.
I prefer the UI and workflow or RT, but dt has better performance on my machine. And RT has this strange longstanding bug where the image is extremely blurry during editing, and only becomes clear after exporting. According to a github issue, a workaround is to disable lens correction (and anything else in the "transform" tab) but this didn't work for me, prompting my most recent switch to dt.
current biggest grip with dt... why are those damn arrows at the edges of the screen so tiny??? Expanding and retracting the side panels requires pixel-perfect accuracy on a ~20px target. I know I could use keyboard shortcuts, but my brain isn't wired for them yet.