Well first off are you talking PvP before 70 and up to, or just level 70?
If you plan on doing what I did/am doing now which is at every bracket stop to do a bit of PvP then it comes down to preference.
I started as a dagger rogue pretty much up to level 40ish. Once I got a couple of nice swords (sword of omen ftw) I respec'd to combat swords then I really started burning through mobs and other players. My damage doubled compared to daggers, sure I didn’t get those lucky backstab/ambush crits anymore but the change in high end damage more that made up for it. (Don’t forget I’m talking pre 70 or even 50 here where you don’t get the gold out of your talent tree yet)
It’s too hard for us to tell you what to go, your best to experiment and then go with what you like.
I can post about how I love swords and then someone else will swear by daggers. That’s not even factoring in skill or positioning while fighting etc.
IMO if you want to be a true rogue as soon as you get to level 50 try out shadowstep. It’s been the best fun I've had in a while and well worth the respec cost.
Having said all that the quickest levelling spec is combat swords, so if you want to get to 70 and then worry about PVP then you can’t go wrong with that spec.
Most of this is in the FAQ, as well as a heap of other things like posions/lockpicking or daggers/maces/swords, what spec’s etc etc.
Well worth the read and prevents the flames.
Good luck
Cheers