If you're planning on keeping the car I'd say go with a rebuilt and you need to make sure it's PROPERLY rebuilt. There's a difference.
A major metro area about a 100 miles away from me has a trade paper that advertises "Rebuilt" RWD transmissions for 300 dollars exchange and about 400 on a FWD. Think about that for a minute and ponder what kind of rebuild it is.
Your current transmission should not be dead at 70k miles so unless maintenance is kept up on the next one it too will have a premature end.
If you go with a used transmission a new torque converter seal and engine rear main seal should also be part of the repair. With a rebuilt transmission the engine rear main should be changed; the trans will have a new converter seal.
This prevents having to tear it all back apart a month later when the engine rear main or a used trans seal starts leaking.