I usually recommend car for getting anywhere around vast Australia, and this is no exception. Sure there are buses that can get you to the Great Ocean Rd, and 'off the beaten track' bus tour companies like Oz Experience, but there are so many great off the beaten track things to see that if you don't have your own transportation, you'll miss a lot.
For the Great Ocean Road, I've heard a lot of people say it's great by motorcycle, and I can imagine it.
The best way to get around The Geelong area ,Is By car with out a doubt.
You can travel around the geelong area by bus. Trains run from Melbourne to geelong on a reasonable sheduel.
despite all this If your not on a coach tour of the area then car is the only quick way to see every thing well.
Or motor bike ,if you wish to travel lighly.
Roads are in very good condition and are all sealed to town ships.
Another great way is to take the queenscliff ferry across to Sorento it takes about an hour.(you can take a car on the ferry)
By car you would need four hours to get there as you would have to go back through melbourne and out along the coast.
Its not as much fun as the Greek ferries but safer and its a really a relaxing trip and as I just mentioned its the quickest way to get to to other side of the coast to see towns like Rosebud and Portsea.
This part of the great ocean road is at least 4 hours from melbourne.
THE DAY this pic was taken was very windy and being very vain I consider it a terrible photo of myself so it is with great personal sacrifice that I put it on .Just so you can see more of the great ocean road.