There are a few things to consider, really.
Talents will affect a lot of which will do more damage. For example, a rogue with improved backstab, improved ambush, opportunity, and lethality will do a lot more damage with daggers than a rogue who doesen't have these things.
Me, personally, I use daggers. I am level 45, but I can ambush for 1100, critical backstab for 700, although, this may be due to my completely backstab-focused talents and a purple mainhand dagger.
Swords do have a higher damage than daggers, but, then again, the two most damaging abilities we have are only dagger usable, (ambush, backstab)
My talents are-
(correct me if i'm wrong about the names/effects)
---Assassination---
Remorseless 5/5 -- 40% increased crit chance for a rogue attack ability for the next 20 seconds after killing a monster that gives experience
Malice -- 5/5 5% increased critical strike chance
Lethality -- 5/5 30% increased critical strike damage bonus for gouge, sinister strike, backstab, amongst other things
---Combat---
Improved Sinister Strike -- 2/2 Reduces energy cost of Sinister Strike by 5 energy.
Improved Gouge -- 3/3 Increases duration of Gouge by 1.5 seconds.
Improved Backstab -- Increases critical strike chance of Backstab by 30% (equalling a total of 50% adding natural crit chance and malice, 90% with remorseless, plus 20% increase from opportunity and 30% dmg crit increase from lethality)
---Subdlety--- (Can't spell right lol)
Master of Deception 5/5 -- decreases chance that something can see you while you are in stealth (doesent really affect dmg)
Opportunity 5/5 -- Increases your damage when striking from behind with Ambush, Backstab, and other stuff.
Improved Ambush -- 3/3 Increases your critical strike chance with Ambush by 45% (plus 20% from natural crit and malice, and 40% from remorseless equals over 100% chance to crit with ambush, plus the 20% damage increase, thats a whole lotta damage, always criting if you can do it fast enough)
The only bad thing to soloing as a dagger rogue is you have a lot more work to do than a sword rogue, but you will do quite a bit more damage. You gotta stealth, get behind the enemy, ambush them before they see you, gouge, run around when its still gouged, and backstab, or, use kidney shot to stun them and run around and backstab them while they are stunned. With 5 combo points, it is possible to pull off two backstabs within 5 seconds of stun. (or you can choose to eviscerate with your combo points). In duels against casters my level, i've killed them in under 10 seconds. One bad thing to choosing this way to solo is that gouge and backstab both use 60 energy, so to do gouge/backstab, you have to be at full energy to pull it off quickly. You can wait behind them for your energy to refill if you didnt start with 100. Kidney shot-backstab only takes 80 energy total, so it can be done with about 3/4 energy. Using these tricks, I am able to solo elites my level, (who don't cast), and can pull off 3-4 backstabs a fight, which isnt bad dps. Although, keeping all of this in mind, it can get really tricky sometimes. Most rogues prefer to,
Equip a sword in mainhand, Cheap Shot, and sinister strike until they stack 5 points, and then eviscerate, and repeat the process. This is a lot easier, but, 1, you get hit more, and 2, it does less damage.
All that said, the real question is if you want to sacrifice a lot more work to do more damage, or you want to take it easy, and do a bit less damage.
____________________________
'Tis but a scratch!