The previous Wrath resigned his position, actually, by siding with the Jedi Knight character. The Emperor has stayed alive through Sith alchemy.
I worded that wrong. I figure (and could be wrong) that there have been multiple wraths. Has there only been two? Scourge and the Sith Warrior?
Still, I'd put the money on the Inquisitor over the Wrath.
For one thing, Inquisitor had the tougher opponent to beat.
Baras was nothing compared to defeating Thanaton in game, if we're going to go by gameplay mechanics.
Storyline wise, Inquisitor survives all that punishement and still came out on top. And I don't know about anyone else, but my LS SI still kept the spirits, except for the one she had a contract with, and one of those was the Voss Mystic
Then let's look at the continuing storyline. Wrath goes about enforcing the Emporers will. Inquisitor goes about gaining more power by collecting artifacts for the Sith, but being the awesome Sith we know the Inquisitor is, that means picking and choosing which ones you keep for yourself and which you give to the Sith Empire to fight over