A crankbait rod will have more of a parabolic action,..meaning a gradual consistent sweep from tip to handle when the rod is "loaded" (think "fish on!!") This gives the rod a softer action and makes it less likely to pull the hooks out of a fish's mouth. With a softer action rod, the fish has time to grab the crankbait and get a better hold of it resulting in better and more consistent hook sets. A jig/worm rod has a faster tip and more backbone. It is designed this way to give the angler the sensitivity required (faster tip) to feel the bait as it's crawled over and through structure and cover,..yet it has the backbone (less parabolic curve)required to give a very powerful hookset and pull the fish out of the thick stuff. Some rod company's catagorize their rods by "action" (i.e, Light,...Med/Light,..Medium,...Medium/Hvy,...and Heavy) and other's use a "power" rating,(i.e. 2,3,4,5,6,etc.)..the smaller the number,..the "lighter" the action. A Crankbait rod will usually be a Medium light to Medium Heavy action and a Jig/Worm rod will usually be a Med/Hvy to Heavy action. I use Medium action Crnkbt rods and Med/Hvy jig/worm rods......both are 6 1/2 and 7 feet in length.
Once you learn the differences in techniques and some of the "why's" as to what rod to use for each technique......then picking/choosing the correct rod becomes a little easier. There really isn't one rod that's good for everything,...but if you HAD to choose one rod for the majority of your fishing needs,...then i'd probably pick a 6 1/2 ft med or med/hvy...you can do a LOT with that rod!! Have fun shopping!!
Mac