We use both. Leaders behind a dive planer would have a swivel and a snap on the mono leader. The main line from rod to lure is a large snap. You need a swivel for spoons or you will suffer from line twist. The swivel on the leader would attach to the dive planer end of the leader. The lure would always get the snap. Crankbaits will pull straight behind dive planers ( the ones without a lip or small short lip ), and large bills just dive and wiggle.