re: Not either or
The Comms network is coming in to place as we speak anyway isnt it?
Odyssey has provided >90% of all data relay for the MER's
MRO will allow a similar volume again.
Both are limited by comms time with each rover, limited by their low altitude
MEX could also be used in this way - and, at a more eliptical orbit could be used for longer passes.
Then, the MTO for '09 will provide a HUGE ammount of relay volume per sol ( >1GB )
Doug