Crankbaits but are expensive and you lose some each time you go. 1.2 to 2mph with idea for me is 1.4 to 1.7 for crappie and i am mainly speaking of Bandits but it is many more that do good.
Road Runners and this won't hurt near as bad losing several of these each trip. Find out how deep the crappie are by asking where you fish, then use them in 1/16, 1/8, 3/16 or 1/4. My favorite is 1/8th size. If you are in the summer months and going deeper, look up big head jigs. They are 1/4th and get deeper. Even when the fish are shallow in the spawn i will leave one or two big head jigs on, troll right over motor and not let out to far. The 1/8ths all around it and let out more. I normally troll 8 to 12 rods. Crankbaits 6 to 8. Speed on big heads or road runners is .07 to 1mph with my favorites at .08.
Pulling creek channels and more open places, cranks are good to use. If you are pulling over alot of mats or shallow water, go with the jigs because you are going to lose some.
You can probably use bigger lb test if you troll 1 or 2 cranks and you get hung up, go back and try go save your crank but this takes precious time from your fishing and you need the lures working. I use 6 to 8lb test on all mine and i keep on going, as it pulls thru the hang or breaks off and you lose whatever you are pulling. Jigs will bend hooks alot and you save your jigs.
I can't really tell no difference on what is best, road runners or bandits. Both good. I know i am using many more jigs these days than cranks because of cost. The cranks, you sometimes catch a bass, big catfish or sauger but this year the road runners have been also. You can cover alot of ground trolling, drops, creek channels, mats, brush, in mouth of bays all good. Pick you some spots and troll and enjoy it. You should find some crappie. Watch depth finder and when you catch a few, remember how deep and try to stay in that depth.