Fresh vs Frozen Broccoli for soup?
I can't imagine there would be a great difference as it's a soup and if you're worried about them becoming mushy then in broccoli cheese soup it should not make much of a difference as they're going to be blitzed anyway. If you were using them though you can keep them from going mushy and keep them green by adding them frozen to a hot pan with just a little water in, stirring often, more here.

Hope this helps!