JPL
For a starting point use the recommendations in the 1979 article matched for film, dilution, light conditions and enlarger type. I have developed Tri-X, at EI 200, 20 C, 1:75, 4 inv each 60s, 14 min. The negatives print at 3 1/2 for my condenser enlarger and paper. I'm not satisfied with my negatives and need to fine tune for both FP-4 and Tri-X. You may get different results than me.
Here is what the The Film Developing Cookbook mentions about the unique tonal quality of Rodinal. "Rodinal negatives possess a beauty and impact that is recognizable their own. Among commercially available developers Agfa Rodinal offers gradation that cannot be obtained otherwise."
So what does that mean? Google "Rodinal Tonality" and you won't a useful definition. Fine grain is mentioned which is misleading. Rodinal is not fine grain but looks fine with 120 film at an enlargement factor of 8X. Creamy highlights are mentioned and reference to a glow.
Last night I ran into a Mike Johnston article
http://theonlinephotographer.typepad.com/the_online_photographer/blog_index.html
I can't find the specific link but he wrote Rodinal takes a zone 5 tone and pulls it down to zone 4. This is what I see. Rodinal compensates in the high tones and can produce pearly highlights combined with darker mid-tones. That may produce print results where a zone 6 highlight surrounded by a dark area appear to glow. I have prints where I see this affect.
I like a hint of ambiguity in my images. One departure from reality is to alter the tonal balance.
Rodinal is no magic soup. But it has properties like sharpness, highlight compensation, long shelf life, and a tonal departure which are different from a general purpose developer.