Both Outlaw and Sub are viable and good in their own ways. It all depends on playstyle and what strategies your team lays out.
For Outlaw, you're going to be more well-rounded. You are the teamplayer. You have extra peels in your pistol shot slow, as well as keeping your kill target slowed.
For Sub, you are more the lone wolf, and your focus is taking out high profile targets WITH your team in mid, as well as playing the objective role. You will have more damage than Outlaw, so use this fact. However, you will lack a slow, so think carefully about the situation.
The moment you shine is when EFC is at 6+ stacks. Sub is amazing at this point. You don't need a slow because the EFC is already slowed from the stacks. You ignore armor because of Gloomblade, so your attacks are more deadly on for instance a druid sitting in bear as opposed to Outlaw not having any armor penetration.
So, if your team is going to play the stack game, you should be sub, if your team is going to play a more rush-oriented style, you should play Outlaw.
For pugs, I still think Outlaw has the upper hand over the other rogue specs simply because it's more well-rounded, and pistol shot helps a great deal.
However, it all comes down to playstyle in the end in terms of pugs, and depends on team in terms of Wargames.