What is the dangerous planet?
Dangerous requires a specification of "dangerous to whom". All
of the planets other than Earth would be difficult to live on
because of their high temperatures, corrosive atmosphere, absence
of almost any atmosphere, crushing gravity, or near absolute zero
surface temperature. Even Earth has areas where your chance of
survival are minimal (at the poles, sea bottom, tops of mountains,
acid springs, volcanic vents, jungles filled with poisonous plants
and dangerous animals.
If the question asks which planet is likely to suddenly leave
its orbit and destroy earth, explode, or hide in your closet to
bite you in the morning - then none.
All this taken into account the most dangerous planet for most f
us is the only one we are ever exposed to - Earth.