Couldn't have said it better myself.
For SMF/phpBB:
A) They're open-source, aka free.
B) They're highly customizable. However, SMF allows you to upload mods directly, phpBB is manually (there are mods that can make it auto, however).
C) They have styles that can make it look just as professional as any other forum software.
D) phpBB boasts a highly configurable permissions system, even styles/themes themselves have permissions. If you call this insecure, you're crazy.
vBulletin:
A) You have to pay for a license, aka not-free & closed-source.
B) It may be customizable, I haven't really used it to know enough if it is or isn't. (I used a cracked version, couldn't get a hang of the admin panel so I let it go)
C) I didn't like a lot of the styles they had for vBulletin...
D) Optimization issues.
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