Lake Garda

You can get around by bus but also by lake ferry service that skips along the shore stopping at various towns. http://www.navigazionelaghi.it/eng/g_illago.html

I've always had a car, but City Buses go all over along the shore. The north lake is my favorite side.
There is public ferry service ( linked by the previous commenter) plus a bunch of private boat operators who organize boat excursions. Having a car has the advantage of flexibility and freedom (you are not tied to a schedule), but you must factor in the cost since the rental charges for vans tend to be exorbitant.

Thanks for the replies. New challenge--What is the best way to get to Riva del Garda from Rovereto if we decide to use the train from Bolzano? I found a bus but it takes 40 mins plus 19 stops. Does anyone know if the is a transfer service or taxi? We are open at this point. The car when you factor gas and tolls is considerably more than trains. Trying to figure it out since there are 5 of us which is he best way to go.

40 minutes is not that bad considering viamichelin says it would take 38 minutes by car. You do have a rather large mountain to go over. I see the no 332 bus that goes from Rovereto train station to Riva del Garda, takes 45 minutes, makes 11 stops, costs about 3 euro per person. Tickets sold at the station. I would think a taxi would be considerably more and you can't get 5 people in one taxi so you would need two.

If you have already a rental car in Bolzano, you might want to keep it. Gas and tolls alone aren't much from Bolzano to Riva.
If you don't have a car already, don't bother. Take public transportation. if the bus is only 45 min. that's not bad at all. I was in Riva (with a car) last summer and the drive from Riva to the freeway entrance (at Rovereto) is about 20 min, so the bus isn't much longer considering that the freeway entrance is closer to Riva than the town (and there is a fast tunnel to get to the freeway).

Thanks, all.