Immigration is normally pretty quick, maybe a 5 minute line. Occasionally I've seen longer lines. Italy has illegal immigration problems with some countries and not with others, and the inspectors seem to single out citizens of certain countries/continents for extreme scrutiny, while waiving others through. If the line is filled with people from N.American and Europe it will move quickly.

I don't intend this post to seem politically incorrect, so I'm dancing around the issue, but If the lines are long and there is a choice of lines, take a look at the people in each and choose accordingly.