I’ve run a number of forums systems from vBulletin to Invision to phpBB and Expression Engine’s (since the first release) and I can attest that EE’s forums are rock solid, dependable, and come with most of the features that users and administrators need. The integration to the rest of EE is decent.
As to user spam, the very nature of forums memberships means you cannot really control the first spam entry. Users sign up on their own and can post on their own. However, I’ve set up EE’s forums so that any posts are also emailed to administrator and moderator accounts, so spam gets identified quickly and the user is either banned or deleted with just a few clicks. Zero tolerance works. Spam comes but it isn’t a regular occurrence, and certainly not much of a bother.
For EE sites in general, I have some with live commenting and others with moderated commenting. Spam seems to come in streaks.