PvP it's magicka sorcerer without any competition. Impossible to die if you play full defence and like a complete chicken.
Templar, followed by DK, has the lowest survivability, even when built as tanks. Lack of movement and escapes, means you always die in the end, when the enemy is successful or if you're brave enough to roam solo. This is why templar + DK's are common in organised groups, but a rare sight among those that solo roam for skirmish or ganking, they exclusively play sorc or NB.
PvE is pretty balanced. As long as you have a good build with some self-healing, doesn't really matter what class or if you're stamina or magicka focused. Can solo most things, including landscape and delves that's supposed to be "group content".