As I have played the Condition and Power builds with my thief, I enjoy the condition build more at the moment. Using D/D, your main damage will come from Death Blossom, but you also have to add in Caltrops, which can max out your bleed stacks if you are lucky (this is through dodging and your skill choice). Also, you do get evasion on DB, 3 dodges instead of 2, more initiative, and the ability to heal during combat. Oh, and to mention you can use Dagger Storm as your elite skill without getting totally dominated. There are so many options and so I promise you that the answer to this question is in your play style. Both builds are fun, but very different.