We will be dropping our van rental off at Piazzale Roma. What is the quickest way for 6 adults to get to our hotel close to San Marco?
The quickest way is a private water taxi. Probably around 75 euros maybe a bit less includes reasonable luggage in price.. You'll see them at the Grand Canal.
Vaporetto would be the next choice. 6.50 euros per person assuming you don't pick up a multi hour pass. Also includes one bag per person
The vaporetto has two lines - one takes 20 minutes, the other 45 to get from Piazzale Roma to San Marco. I took the slow boat and listened to Rick's free audio guide for the Grand Canal along the way. The rest of my stay in Venice I walked, so I'm glad I took the Canal tour. I would have preferred to have done the ride without my bag, but it worked well enough.
The vaporetto has two sections - an open, standing section and a closed in (with windows) section with seats. Because I had my bag I was in the seated section. I would have liked to have been in the open air to see better, but it was still okay.