Simple Machines (SMF) has a slight or maybe huge advantage with the fact it has a theme and mod installer built in. Note, even XenForo, a premium brand, doesn't have that. Now, looking at MyBB, we see it has a rating system installed. There is no need for a mod to get it. Finally, phpBB has an alert system, something missing from SMF and MyBB.
Anyhow, what pros and cons do you see with these free software brands?