Calling all Northern Rhone enthusiasts, stylistically speaking, what do you think the differences and similarities between these two regions are?
What are some of your favorite producers within them?
I definitely give credence to what Geoff is saying, but I would need to do a little research to see if correlation does in fact lead to causation, i.e. if it's more of a wine-making and vintage thing here in some instances, but I do think you can break the wines produced in these two appellations down in to two major stylistic camps.
First, you have your black fruited, rich, juicy producers (a la Cornas) - Gonon, David Raynaud, Graillot, Voge, would all fall into to this camp for me in most vintages versus the more red-fruited, floral/quasi-Burgundian producers (a la Cote Rotie) - Faury, Souillard, and Vincent Paris' wines are generally more this direction for me. I will say, in general, most St. Jo producers trend towards the more Cote Rotie-end of the style spectrum, and most Croze producers trend towards the more Cornas-y end of the spectrum, but again, take that generalization with a grain of salt.
Most of the critical literature (especially Jonathan Livingstone-Learmonth, who's probably the greatest living english-language authority on the Northern Rhone) does say that the highest quality producers have vineyards located on the backside of the hill of hermitage in Croze, and in St. Joseph, most of the quality producers work in the southern-most section of the appellation around Mauves.
I don't understand what you mean by correlation and causation in this instance. Are you saying a variety of site geography doesn't necessarily cause a variety in wine quality?