Although I’ve played around with it a bit and even written a few blog posts about it, I’m not really an R user and barely rise to the dilettante level. andyptt21 over at The Scientific Shrimper is an R user with several years experience. Like most R users he started out with Rstudio and used it for four years before he replaced it with Emacs and Org-mode.
In a blog post, Soapbox Rant: Why I use Emacs for R programming, he explains why he made the switch and why he thinks it was the right move. He finds that Emacs is more flexible with respect to window arrangement and is, of course, customizable so that you can make editing/experimenting experience just the way you like it.
He’s also discovered—as many of us have—that using keyboard navigation so that you never have to take your hands off the keyboard is a real win over using a mouse for the same tasks. This seems counter intuitive and always surprises people when they discover it.
He gives a few other reasons for the switch—including the integration with Org-mode through Babel. If you’re an R user, you should give it a read. Perhaps it will convince you to make the switch as well.