Yeah, I made this thread months ago and I got super flamed. Karma is simply more reliable. You can count on her damage being enough and her ability to find strength in protection is invaluable. Laning with a gap-closer gives you amazing harass, and the shieldburst allows gap-closers to not only harass but be shielded from all the damage thrown at them while retreating.
And to the above post, I disagree about range. Yes, Ori has more actual range, but Karma's shieldburst allows her to damage all enemies in a large radius around her target, roughly equal to its cast range. So you can utilize double her range if played correctly. If the enemy is farming (which they undoubtedly will) a shieldburst on a minion can be done from far away in a bush, and still damage your target.