I am often asked to make a recommendation regarding which style of lock nut to use. I will start by saying that the answer to that question is not easy! The two most common lock nut groups are the Prevailing Torque Group and the Surface-bearing Group.
In the Prevailing Torque Group, we carry the nylock insert locknut and the all-steel stover C grade 8 lock nut. In the Surface -bearing Group, we carry the serrated flange nut and the Keps nut. (K-Lock)
All of these are good effective locknuts when used in the right context, but the decision is yours as personal preference is what dictates your decision.
Here are a few considerations:
Temperature: Obviously you would not use a nylock on an exhaust system since the heat would melt it.
Size and shape of the hole: If the hole is oversized, a flange nut is a great way to go versus a flat washer.
Length of thread exposure: Top lock versus center or bottom lock
Re-use: An all-steel nut is harder on the threads of the bolt than any of the other styles.