Numpy argsort vs Scipy.stats rankdata

Question

I've recently used both of these functions, and am looking for input from anyone who can speak to the following:

• do argsort and rankdata differ fundamentally in their purpose?
• are there performance advantages with one over the other? (specifically: large vs small array performance differences?)
• what is the memory overhead associated with importing rankdata?

Thanks in advance.

p.s. I could not create the new tags 'argsort' or 'rankdata'. If anyone with sufficient standing feels they should be added to this question, please do.