Depending on your weapons, strength or dexterity. Seeing as you're using a dagger, go all in dexterity or unless you're having trouble soloing stat some into Vitality.
Spec into Backstab. Do not use cast abilities as they will not charge using your melee weapon.
check here to find out the weapon ratios (whether to stat str or dex):
http://ladderslasher.d2jsp.org/index.php?g=3 This post was edited by Clacks on Jan 2 2013 10:31pm