keyrunning:
High end: sorc
mid: sorc
low: assa
With low gear the sorc will not be able to teleport safely, while the sin can still run, a bit slow but safe. Once you get hold of moderately good gear the sorc can tele relatively safe, while the assa still can't tele well until she get high end gear, therefor the sorc wins.
None will have any problems surviving in high end gear, but the sorc will be faster because of faster tele.
When comparing their damage you have to consider that the sorc can benefit from -res while the sin can't apart from lower res and/or conviction. The assassin gets ds to help with crowd clearing. The sorc will be faster at killing bosses without doubt thanks too static.
In pvm a high end sorc will be faster for mfing then a high end assa. In pvp stunlock and the other skills of an asn gets to shine giving her an edge there.