Having someone to call is very important. It means responsibility. FOSS sounds good, especially some popular stable projects. But do they fix bugs following your pace? Do they add features when you ask? Do they test everything before release or they let you test it?
I personally work for a proprietary software company. I would suggest your company go with the proprietary software. Because you have someone to call where bugs happen!
Well, bugs happen, and you will need to upgrade in the long run. Does your boss call you to work on it? If so, fine. If not, or you don't want to, go with proprietary.