The advantage of driving to Bondi Beach would be that you can come and go when you want and take more equipment like beach umbrellas, picnic baskets etc.The major downside is the limited and expensive parking. You can park all day in the beach carpark at Queen Elizabeth Drive for $7 per hour. On a weekday you'll probably get a spot but there is no guarantee. The limited parking on the surrounding streets is restricted to 2 hours maximum by expensive parking meters and the local council has an army of very diligent parking inspectors - fines are exorbitant. There are free parking spots to the north as you move further away from the beach (at least 1 km).

Public transport would be by train and bus - google "Transport NSW Info" and use the Trip Planner. The trains and buses you would use are frequent and reliable - I'd estimate a travel time of 75 to 90 minutes.

As a local I'd probably take a chance and go by car, but if you are an overseas visitor the public transport option has less potential problems in what is an unfamiliar city.