Probably a BSD will suffice. Linux has the market momentum, so if third-party products are an issue, it might be the OS for you. You can also try the Linux emulation modes on the BSDs. If you're going to have to hire somebody or train somebody, Linux has the most training material. While many are sharing strategies to make Linux install more easily, it tends to be less stable.
Every release has a lot of new code - and new problems.
These bugs might not be a big issue if Linux is merely running a firewall-protected desktop system, but they could be a showstopper if it's your Web site. Whatever OS you choose, you'll need knowledgeable people, and they'll need the time and resources to run a secure site. Work with them to determine whether you've made the right OS choices, and consider changing if you got it wrong the first time. He works with databases, Web servers, e-mail, application development and system administration.