To my mind, there's no question: it's got to be daggers. I'm a longtime D&D player, and Rogues are supposed to Backstab, and Ambush, and sneak around and get in positions to do huge amounts of damage. A poisoned dagger is a Rogue's specialty, and that's what he's got to be wielding.
On the other hand, some Rogues can't handle the pressure of stealth-- they equip swords and go in swinging for the fences. Don't get me wrong-- there is a lot of good in a sword spec. Combat is basically the best solo spec you'll find, and Blade Flurry is pretty much a Rogue's only weapon against multiple opponents.
But even though it actually makes soloing harder, to me, a Rogue's just not a Rogue without a dagger in the main hand. You sword Rogues can disagree (and I know you will-- a sword-loving guildie of mine has argued this with me many times), but if you're not interested in sneaking around behind your target, and burying that toxic dagger in his back, maybe you should have rolled a fury Warrior.