Just go Assasin. Juggernaut is top-heavy, and shines only with gear. Not even mentioning that it can take a lot to get used to in terms of resource management and skill usage.

Sin, on the other hand, is rather forgiving in terms of both, survivability and resource-management. It does respectable damage, even in Darkness (tank) spec, which, when hybridized with Madness, is one of the strongest specs there currently are. Before each fight, you can almost always mind maze the strongest enemy and take apart the weaker ones.