Hiring a car undoubtedly gives you more flexibility, but it is quite possible to have a great holiday on Lake Como without your own transport, as long as you choose a base near to the ferries and a major bus route. Both ferries and buses stop running around 8 in the evening, so taking the public transport option does mean that you will need to be back at base in time for dinner, unless you are prepared to push the boat out (perhaps literally!) for a taxi.
If you are based in or near Menaggio, and you just want a car for a trip on one or two days, you can hire from the garage opposite the ferry terminal.
Follow these links for more information about driving, and for public transport: buses, ferries, trains