Generally for aircraft, what is the most hazardous kind of thunderstorm?

A squall line thunderstorm is considered one of the most hazardous types of thunderstorms for aircraft due to its extensive and organized nature. These thunderstorms can produce severe weather conditions such as strong winds, hail, and intense precipitation over a large area, which can lead to significant turbulence, low visibility, and other dangers for pilots.

Squall lines often develop in advance of cold fronts and can extend for hundreds of miles, creating a long, continuous line of thunderstorms. The straight-line winds associated with squall lines can exceed 60 knots, posing a substantial threat to aircraft during takeoff and landing phases. In addition, the possibility of severe downdrafts and microbursts, along with the potential for strong vertical wind shear, makes these storms particularly hazardous.

Other types of thunderstorms mentioned, while still dangerous, typically do not present the same level of widespread and severe weather hazards as a squall line thunderstorm does, especially in terms of their organized structure and the strong, damaging winds that accompany them.