... that you like to use, and that gives you the best opportunity to get the bait into the strike zone. Finding where they are, or knowing where they are, should be your first priority. Second priority is to pick which method to use, that will present the bait in the best way, and the easiest way for you. Methods of presentation that you "can" use, depend on your equipment and boat setup.
As to your questions on specific types : Generally speaking (IMHO) -
Spider rigging, trolling, strolling, side pulling ... when you need to cover large areas of open water.
Dock shooting - year around, depending on water depth.
Fixed bobber - when you can fish a depth less than the length of your rod.
Slip bobber - when you have to fish a depth greater than the length of your rod, or when casting.
Casting - whenever & wherever you can get your bait to the proper depth, from a distance.
Jigging/Vertical Casting - whenever & wherever you can get your bait to the proper depth, from the distance that your rod length allows.
Alot depends on the body of water you fish ... what it has in the way of depth, cover types, baitfish types, water temp ranges thru the seasons, what type of body of water it is, whether it gets a thermocline or not, what state or region of the country it's in, it's biomass capacity, normal water clarity, and the prevailing conditions at the time you fish.
Crappie are going to be "where they are", for a reason. If you know, or can figure out "where" they are or are most likely to be, then picking the proper method of presentation will be easier. Crappie move around, in search of food, but also to stay in water conditions to their liking (but, would rather not have to). They're like us, in a way ... they want security, comfort, and an easy meal. If a situation/condition exists, that affords them all of these ... they're very likely to be there.
Black Crappie & White Crappie do have different criteria, and that can be a factor in "where" they are at a given time and under given conditions. So, it can be a factor as to when/where you look for either of these. They can also be found in the same place, at the same time (depending on prevailing conditions).
The more important question to ask, would be - "Where are the Crappie most likely to be, during a specific time of year, in a specific body of water, under the current conditions of that body of water ?" When you get the answer to that question, then you should ask yourself what method to use to get the proper bait presented in the proper way ... to interest the fish into biting that bait. The answer to that question is only limited to what methods you are able to use, given the equipment you have, and the speed/depth needed to present the bait to the fish, under the conditions of the place they're residing.
... cp