6 and 66 go over Wong Ngai Chung Gap, with the more exciting ride and interesting scenery. 6 goes to Stanley Market while 66 goes to Ma Hang (closer to Murray House); for tourists, either is fine.
6A, 6X and 260 take the Aberdeen Tunnel, with 260 taking Gloucester Road to bypassing Wanchai as well. The scenery is not that bad either, passing through Deep Water Bay.
I'll say all the buses take about 45 minutes. Taxi about half an hour. It's about 16km, so taxi fare about HK$120.