I think Venice is really tough if you do it on a day trip during the summer. It is hot, crowded, and likely smelly. I like Venice in October the best. No matter when you go, I think it is really important to stay the night in Venice. It is a different place once the day trippers all leave.

I agree with Pisa. It is basically a field with a Church, baptistry, and tower. No charm whatsoever, but lots of crowds.