Abyss 17 + 1 = 18 Every possible nasty environment you can imagine ... if you can lure the PCs in, to experience it
Acheron 12
Arborea/Olympus 22 - 2 = 20 Maybe there is something good about this plane after all; it keeps bouncing back after I downvote it.
Arcadia 11
The Nine Hells 19
Beastlands/Happy Hunting Grounds 27
Carceri/Tarterus 16
Elysium/Blessed Fields 26
Gehenna 10
Gray Waste/Hades 9
Pandemonium 9
Ysgard/Gladsheim 20