The most basic difference is that one is linux and the other is BSD. Linux by it's very nature is a mass compilation of thousands of software projects whereas BSD is a far more centralized "professional-like" operating system.
In short - BSD will probably be more stablke as all of it's core components are developed and maintained internally, whereas linux will be more versatile as it is designed to work with various different types of software.
Go to the BSD forum, read the "Before you post thread" and follow the link to an essay explaining the difference between the two.
Other than that, both projects seem to have the same goals, and as I have not used either, I'll say nothing further.