Welcome Cliff, glad to have you here. I too am learning about the qualities of different wood for smoking. I myself have tried Hickory(careful with this, it can get out of hand fast), Oak(not bad, havent decided on it yet), Mesquite(pretty good) but I have grown fond of the fruits such as apple and citrus. Apple has a smooth and yet mellow flavor great for porks, and citrus is a bit bolder but not extreme, great also for pork, but my family loves it for chicken. As for pecan, I know I am very allergic to pecans. Thus I have never tried it to smoke with. The best I can say is try them all with each of your meats, flavor changes with amount of smoke, time, as does the rubs and sauces used. So experiment a bit and see what you like best. I have also heard some mix the woods for various flavors. Have fun, and dont be affraid to ask, we will gladly have an answer for you.
Rob