I understand. I believe I pointed that all out my comment above. I wasn't saying that I find the notebooks superior because they allow for rich & dynamic output, but that I find it superior to RStudio when all you want is a quick exploratory REPL capable of rich/dynamic output. I simply find it easier to fire up a notebook and start noodling around than writing an RMarkdown notebook. That really only holds if I'm not overly concerned with keeping or sharing the notebook. Otherwise, I believe RMarkdown is the better option.

I also tend gravitate towards ESS, and probably split my R development time between emacs and RStudio. I've even written a very kludgy Rmd notebook mode that uses overlays to show evaluation results from code chunks. But RStudio is very well-designed and ESS just doesn't compare feature-wise, sadly.