There are a host of chile peppers ranging from mild to searing. In general, the larger the pepper, the milder its flavor. Thus the chile used for stuffing is quite mild. The smaller jalepeno is hotter. The chile pequin - about the size of a small raisin - is blistering hot. There may be dozens or even hundreds of different hot peppers. In this site, we will generally treat the fresh pepper as produce and the dried pepper as spice.
The Relleno chile is called an Anaheim pepper when it is fresh; when it is dried, it is called an ancho chile. Ancho chile is the brown powder that is central to the creation of the stew we know as chili. This same brown powder can be used in a host of preparations to add depth of flavor. Almost any dark meat sauce can be improved by it.
Jalepenos can be used fresh red or green. Ripened jalepenos are smoked and dried to create chipotle chiles. These can be purchased in jars or ground into chipotle chile spice. Nothing imparts quite so complex, warm, and smokey a flavor to meat and bean dishes as a pinch of chipotle chili. It's highly recommended. Serrano chilis are slightly smaller and hotter than jalepenos.
The hottest peppers are the scotch bonnets or habaneros. Beneath their searing heat is a rich, buttery or nutty flavor that complements almost any meat or vegetable dish. It is clearly discernable in Melinda's hot sauce.
In the case of every pepper, If you want the flavor of the jalepeno with less heat, carefully remove all of the ribs that hold the seeds in place; the heat in peppers is strongest in these light colored ribs.
Here are some strategies for treating chile peppers effectively in recipes.