If you want to kill in a single hit the highest damage weapon is the best, so that would be Twinkle out of your options. The DoV is good for shutting down mages after you stab them but don;t manage to kill them.
Isn't there a similar thread a bit further down? Please help fight redundancy!
On that note: @Eudaemonium is correct, you want a high base damage to be multiplied by your backstab. Special procs such as the poison on Dagger of Venom are useful, but don't get multiplied by backstab.
Twinkle. It'll be better than most of the staffs you can get in the game (with backstabbing) and provided you have 95 in pick pockets you can pick it off Drizzt (or you could just kill him). So you'll get a lot of use out of it.
Comments
On that note: @Eudaemonium is correct, you want a high base damage to be multiplied by your backstab. Special procs such as the poison on Dagger of Venom are useful, but don't get multiplied by backstab.