Which type of supercell is most likely to develop into a squall line during its later stages?

Answer 1

You probably are referring to HP supercells, or "High Precipitation" or "Heavy Precipitation" supercells. In the summer, we see a lot of these develop and cycle through their lifespan very quickly here in SW Florida. Beautiful to watch.

Answer 2

HP. The outflow of the HP supercell cell is the strongest of the three types. DBZ is not a type of supercell. As the outflow spreads out, it can trigger new thunderstorm development.