All of the weapons that scale to 19 have the same weapon damage and speed as far as I know. So any dungeon drop or heirloom are going to have the same weapon damage. For (outlaw) rogues, generally we want a lot of damage output over survivability. Which means agility is top priority. Shadowfang and bronze shortsword have 6 agility, making them really good options (with shadowfang's proc making it slightly better). Cruel Barb (5agi/3crit) is another solid option. Theres a number of options like "Thief's Blade" that are basically of the quickblade - which are solid stats.
For mainhand though, weapon damage is king. And the blue BG crate weapon is higher ilvl and has higher weapon damage than any (non-grandfathered) weapon, making it BiS. Ideally you also get verse/crit as secondaries. Until then, all of the 19 scaled weapons have the same weapon damage, so it would then be stats that we care about - so we can basically use the same logic as we would use in choosing an offhand, which is...
For an offhand, we want the most agility/verse. Shadowfang is BiS offhand. Bronze shortsword is close behind. Since bronze shortsword is so easy to get, I haven't included a lot of the other "almost as good" options like Thief's Blade.