Personally now I have to say I love all 4 solid white snakes. BELs, BLackELs, Snows, and Albino Super Black Pastels.
The BEL complex morphs are: Mojave, Vin Russo, Lesser, Butter, and Phantom. However the only ones that produce supers that are BELs are Vin Russo, Lesser, and Butter. The Super Mojave has a distinct graying of the head and the Super Phantom isnt a white snake. I'm not sure about Vin Russo being bred to the other 4 or Phantom being bred to anything but Lesser, but any combination of Butter/Mojave/Lesser will make a BEL. In my opinion you should not breed Butters and Lessers if you arent an expert on them because you'll have a heck of a time distinguishing which offspring are which.