I liked the following comment from the old thread, written by mavam:

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(Disclaimer: Bro team member)

First, Bro is a Turing-complete scripting language ("the Python for the network") and Snort/Suricata a system centered around regular-expression matching [1]. These two paradigms have fundamentally different levels of expressiveness.

Second, Bro's core is policy-neutral. [Continued at https://news.ycombinator.com/item?id=7728850].