In the strict hierarchy of medical land the epitome of medical wisdom is the full fledged consultant - corresponds to Chefarzt. Then comes the top tier of underlings, i.e. the associate consultant - Leitender Oberarzt.
More towards the peons you find the assistant consultant (if there is such an animal) - Oberarzt (actually we are the guys who do most of the work, sort of like the linebackers in football, unsung heroes and all that ;-).
Facharzt does not really correspond to consultant; the latter breed really is top notch in their field while Facharzt would correspond to registrar in the UK or staff/senior staff member in the US.