My department supplies us with Thorogood Commando boots. They are by far the worst boot I have ever worn. I ended up purchasing a pair of danner Acadias with the zipper inserts. They are a superior boot and have never had a leak of water when I was standing in 7 inches of water at a wreck scene.
My F.D. issues us Redwing boots with zippers or Rocky Eliminators, both with steel toes. Some guys wear their own boots though. As long as they have steel toes I don't think anyone really cares.