Personally I find it very difficult to distinguish between the wines of these two appellations and I love both. The grower house style tends to over-ride any differences between the communes and as far as I know there are no reputable houses which do both so as to permit a valid comparison. Additionally within both appellations there are different soil types; argilo-calcaire (calky clay), argilo-siliceux (flinty clay), graviers (gravel), sables (sand) and graviers sablonneux (sandy gravel). The clay terroirs tend to produce fuller bodied wines more suitable for keeping and the sand and gravel lighter fruity wines for early consumption though some of Alliet's wines, for example, from Chinon sandy gravel are quite powerful indeed.
Amongst the Chinon growers I can personally recommend Bernard Baudry, Philippe Alliet (more heavy and sometimes somewhat oaky though integrating with ageing), Charles Joguet (more classical and ageing beautifully in his top Doiterie and Chêne Vert cuvées). For Bourgueil and Saint-Nicolas de Bougueil, Yannick Amirault (some find them too "modern" but I like them), Druet, Domaine de la Chevalerie (Pierre Caslot) and Jacky Blot (better known for Monlouis and Vouvray under the name Domaine de la Taille aux Loups).
I don't know about availabilty and prices in the USA but over here these wines represent excellent QPR with hardly any costing more than 20 EUR.
While checking out Loire Cabernet franc based reds, don't overlook Saumur-Champigny about 40 km to the West in Anjou. There are some wonderful wines here too, perhaps a bit fuller bodied and tannic than Chinon and Bourgueil.