The way I was taught by my Master way back when was that 2 layers of non-adhesive varnished cambric tape goes on first to keep the connection clean for future access. Then 4 lapped layers of non-adhesive rubber tape goes over that to provide the primary insulation and moisture seal, because the rubber fuses over time and becomes a solid mass. It also provides some added resistance to abrasion against the peckerhead under vibration. Then 2 layers of adhesive PVC tape goes over the rubber because it's immediately adhesive, whereas the rubber will unravel before it can fuse if not covered. The PVC tape is also run down along the conductors at least 2 laps past the rubber tape to ensure the seal. I used to take apart a lot of old motor connections and when the cambric wasn't used, it was a mess to clean up the connections when it came time to make them up again.
In addition, I was told that the rubber will break down from the ozone that happens around the magnetic fields of the motor windings and the PVC will seal that out. I don't know about that last part though, I think that may be a relic of when people used a lot of brush type DC motors and maybe Universal motors, because ozone tends to come from arcs, and there shouldn't be any arcs in AC motors (except maybe Wound Rotor and Synchronous motors).
Split bolts vs ring lugs and bolts vs mechanical lugs; it all depends on the size of the motor. Generally we used ring tongue crimps with nuts and bolts for anything wired with #10 or smaller, then split bolts up to the point where motors came with their own mechanical lugs or studs. But I only worked on industrial plants, so we were NEVER allowed to use "wire nuts" anywhere other than in office receptacle and lighting j-boxes. IIRC, they are not allowed under NFPA79, which for an industrial facility, trumps NFPA70.
Mind you I have not been making up motor connections for a few years now, so I have no need to keep up with new product developments, but I have seen some cool stuff being peddled now.
