StreamOfTheSky
Adventurer
Nifft said:(Note that the OP called out planar travel, so spellcasting seems practically required.)
Multiple people have named Monk. Druid has gotten the most votes and doesn't even get planar travel. So clearly, more than one interpretation of what it means to be survivable. Not to mention how situational. City overrun by gangs or lifeless wilderness, for example. Requires completely different abilities. For overcoming and survivng the nastiest fights imaginable, I'll put my money on the Crusader. Hey, some enemies even lay down dimensional anchors and such, so you can't just run away!