Types of Fly Rods:
Graphite Fly rods are now considered to be the "state of the art" in fly fishing today.
The use of graphite in fly rod making is fairly new. It started in the late 1970's. When compared to the fiberglass and bamboo rods that were most common before graphite, graphite is much stronger and considerably lighter. These two factors alone allow manufacturers to make longer and thinner rods that weight less. Because graphite is also stronger, it creates more "power". Power equates to line speed that increases the ability to cut the wind, increase casting distance and the energy to cast heavy flies and sinking lines.
Graphite fly rods have a "faster action" than do glass or bamboo rods. The speed at which a rod returns to a straight position from a flexed or bent position is termed "recovery rate". Recovery rate is is what determines if a rod is fast or slow. A fast recovery rate significantly contributes to casting tighter loops. Tight loops improve your ability to cast in the wind, increase casting distance and accuracy and put your fly into tighter spaces such as under overhanging branches.
Graphite has also allowed rod designers to develop a multitude of different tapers and strengths by combining different kinds of graphite fibers and resins. This has led to many of the newer "specialty" rods like the longer "Euro nymphing" rods and the "switch" and spey rods.
Some say, and I agree, because graphite is stronger and stiffer, the butt section is also stronger and stiffer and this provides a better rod for fighting and landing larger fish. If you are proponent of catch and release, this should be an important consideration in rod selection. If you can more quickly and effectively fight and land the fish, the better it is for the fish that you intend to release.
In recent years, Winston has begun offering a line of fly rods that incorporate boron into several of their rod designs.
Fiberglass had a long run as the material of choice for fly rods. As newer and better fiberglass materials have become available, fiberglass rods are undergoing a strong resurgence with some groups of fly fishers.
If you do a bit of reading and talk to some of the "glass guys", you discover that, in their view, fiberglass has a number of advantages over graphite in certain circumstances/situations. Because glass rods have a slower action, many feel they are easier to cast. "Feel" is a term used by many of the glass rod advocates. They describe "feel" as the ability to easily feel the rod load. "Presentation" is another stated benefit of glass rods. Because the rods are slower, they tend to generate slower line speeds and "glass guys" will say that translates into a more delicate presentation. I have read several articles that talk about the toughness of fiberglass as compared to graphite. The toughness relates to the rods ability to bend more without breaking and also its ability to survive physical abuse that might break a graphite rod. As a general rule, fiberglass rods are less expensive than their graphite equivalents. See more on fiberglass rods here...
I have heard several of my more knowledgeable "bamboo buddies" say things like "graphite is for shooting line and bamboo is for casting line". For this group that is all that needs to be said. Personally, when I think fly rod...the picture in my mind is an old classic bamboo rod. I have had a couple of fishable bamboo rods that I really enjoyed fishing on small streams with small dry flies. I still have one but it sees very little action as I have relegated it to the closet in favor of graphite.
In terms of bamboo as a rod making material, it is heavier than either fiberglass or graphite. Bamboo rods tend to be much shorter than either glass or graphite rods...I guess this is to keep the overall weight of the rod to a minimum. Generally, bamboo fly rods fans favor many of the same things that the "glass guys" do...a slower action. Slower rods do produce slower line speeds and this, many say, leads to a more delicate presentation. See more on bamboo fly rods here...
Spey rods get their name from a style of fly casting that was developed in Scotland in the 1850's on the River Spey. Spey casting is primarily used for fishing large rivers for salmon and large trout such as steelhead and sea trout. Spey technique is also used in saltwater when fly casting in the surf. All of these situations require the fly fisher to cast large flies long distances in order to cover a lot of water. The two-handed Spey technique allows more powerful casts and avoids obstacles on the shore by keeping most of the line in front of the angler.
I will readily admit that I have never touched a switch rod so I have little to say on the topic. I do know that switch rods are becoming increasingly popular in certain fly fishing communities. Based upon my reading, a switch rod is a hybrid between a traditional fly rod and a spey rod. We all know what a traditional fly rod is. So what is a spey rod? Simply put, a spey rod is a very long two-handed fly rod. Spey rods have many advantages in certain fly fishing situations.
Here are some links that will help you better understand the benefits of switch rods:
What is a switch rod? (Globalflyfisher.com)
Spey vs Switch Rods explained (video) by Tom Larimer (Trident Fly Fishing)
Switch Rod (video by Red's Fly Shop)
Switch Rods - Why You Need One (by Alaska Fly Fishing Goods)
What is a Switch Rod and Should You Consider One? (by trout-fly-fishing.com)