The Thief build gets a +1 to attack rolls with all rogue weapons at level 2 and also gets a +2 to damage with the Weapon Finesse class ability that scales up with later levels.
You can go more accurate and use the heavy blade, but you really want to grab the Fullblade if you go that route for the d12 and high crit (you either get Fullblade & WF for same as above, or Fullblade and WE for +1 more to hit and -1 damagel)
There are no superior weapons in Essentials, at all.
That doesn't make them inaccessible if you have the books or CB.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.