Unlike spin fishing — in which the weight of a heavy lure propels its trajectory — the fly fisherman uses a weighted line to cast a nearly weightless fly. So graphite rods come in varying lengths and weights (from 0-14) to accommodate the corresponding weights of line. Weight rods (0 to 4) can be used for tiny fish (like panfish) while a size 14 is made to accommodate big saltwater game like marlin.
For most freshwater fishing, Rosenbauer suggests splitting the difference and going with a rod in the 4- to 5-weight range that is 9 feet long (the typical size that works best for most circumstances). "Four or five is standard for trout and pan fish," he says. "If you're gonna put bass in the mix, and some very light saltwater fish, you might want to go with a 6-weight. You can still fish for trout with a 6-weight, too." Just be sure you actually test out the rod first. "You can't tell much from looking at a rod," he says. "Whether you're out with a guide or you're in a store with a buddy, you want to try the rod first. You don't buy a car without driving it. A good fly shop will have lots of rods available, and you'll be able to go outside somewhere and test it. If a fly shop doesn't have the ability to let you test out a rod, then I wouldn't go there." We recommend looking for a light rod that can still deliver strength and pinpoint accuracy, such as the Orvis Helios 2. [$800; amazon.com]