I would certainly go for BES as it will give you all the features and centralized management you need. It isn’t hard to install. Put it on its own server and give it an account with exchange admin privs so it can see everyone’s mail.
While you can certainly run into some issues with Blackberry’s BES Server, overall, it is really great. At my company, we have about 50 users on it and have had very few issues over the past 2 years.
By the way, it is “Blackberry”, like the fruit.
Thanks for the question!