Paralysis is always a good choice, if you have the ingredients handy. I'm also a big fan of Damage Health, especially if you have Concentrated Poison. Status effect poisons don't get a lot of benefit from Concentrated Poison unless you're fighting multiple enemies, but it straight up doubles the uses and thus damage of Damage Health poisons. The fact that the damage is instant also helps, lingering poisons are fun but can allow your target enough time to alert his friends.
Paralyze. I'm addicted to it. Did you know that if you kill someone with an arrow poisoned with paralyze, their body looks like it has rigor mortise or something and locks in weird positions? I'm playing a char right now that is secretly an assassin whose trademark is that all of his targets are killed with arrows poisoned with paralyze. It's a cool trademark. :)
Hopefully none of your targets are vampires :). Then again, you could still kill them with poisoned arrows just for the hell of it.
I wish there was a perk in the Alchemy tree that removed or reduced your target's poison resistance. You could probably roll it and Snakeblood into the same perk really. It would make Dawnguard a lot easier for alchemists, no doubt. I keep wanting to put damage health poisons on my crossbow bolts until I realize that it won't do anything. Stupid vampires and their stupid poison immunity. :(