im mainly a bass fisherman and heres what i have learned about rods diffrent sizes, and diffrent stiffness...if your fishing plastic baits, like texas rig carolina rig worms etc, its good to have 6 6 to a 7 foot medium heavy rod and a relatively quick ratio reel, 6:4:1 reels are a happy medium, and will serve the purpose to anything your throw pretty much. Medium heavy rod allows you to set the hook better when worm fishing and you dont have too much bend or flex.. Top water fishing, such as flukes, pop rs, zara spooks etc i like a 6 3-6 foot 6 medium fast rod, i use a 6 3 skeet reese, 6 4 cashion medium fast, and a kistler 6 6 medium fast for topwater baits, and a faster 7:1:1 ratio reel, on top water when ur working the lure, its jerk, pause, jerk jerk, pause and this creates alot of slack in the line, when you get a strike, the fast gear ratio reel helps get the line in quicker to set the hook!
Crankbaits i use a 7 ft medium lews rod with a slower ratio 5:4:1 reel, crankbaits u need a "flimsy" rod with a lil bend in it to allow the fish to take the bait and ur not ripping the treble hooks out and away from them...stretch, bend, then set the hook, make sense? I havent fished much with swimbaits, but some of these things are huge and alot of people prefer 7 4 7 6 heavy rods..Again, its all personal preference but this is kinda a guide line to bass fishing rods and info i have learned over the years...Heres a diagram describing the diffrent "speeds" of rods.