Revenant (Human), probably warden.
With the ability of revenants to stay concious while below 0 hitpoints, the bonus to saves you can get from human etc, you can create a character that only ever dies if he gets to negative bloodied hitpoints... and he'll be getting over 20 on his death saves probably about half the time for a free heal.
Elf Archer Ranger - They can simply move farther than nearly all the enemies and can out range almost everything especially with a greatbow. In close combat they just zip in and out of superior cover making them all but impossible to target for most things. By far the toughest to hurt/kill without specifically designing areas or encounters to weaken them.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.