Weight
Denim is weighed in ounces per square yard. Under 10 oz is light and soft, good for shirts. 12 oz is the everyday middle. 13.5 oz and up is heavy: stiffer at first, longer lasting, and it fades with contrast.
Weave
Most denim is a right-hand twill. Selvedge denim is woven on a shuttle loom and has a finished edge; it is not better by itself, but it usually means slower weaving and better yarn.
Wash
Raw means unwashed: dark, stiff, and yours to fade. Rinsed is washed once to remove the stiffness. Stone-washed has been tumbled with pumice for a worn look. If you want a pair to look like yours, start raw.
The short rule
Buy the weight you will actually wear in the weather you actually have, and wash it as little as you can bear.