I would definitely drive.
To take the bus, you would need to:
1) Take bus from Pop to either MGM or another Park.
2) If you went to MGM, take the boat to Yacht/Beach Club or take the bus from another park.
3) Afterwards, take a bus (or boat to MGM) back to another park
4) Change buses to Poly or take monorail.
Another option would be:
1) Take bus to Epcot.
2) Walk all the way through EPCOT to international gateway and then walk to beaches & cream.
3) Walk all the way back through EPCOT
4) Take the monorail.