The title says it all. It's not a flame thread similar to "nVIDIA vs ATi" or "AMD vs Intel", as board software is pretty much conserning many ppl's private info, thoughts, which are "written to remain" and "be remembered" in some way. There are many both technical and not so technical (influenced by personal preference) articles on the net regarding this subject, but what's your opinion? Usually phpBB is being used because it's free, but it has proved to be the most insecure one, it's not "free" like Linux for example. I personally have administrated phpBB(I hope I won't have to do this again) and am currently administrating 2 vBulletin boards, so am not so familiar with IPB, just looked once or twice through its code...well, it's written in a shitty way for a professional software, and still can be compromised with a sniffer through the 'Report post' function. You can clearly see where I'm heading - vBulletin is the best board software for me and is worth every peny. It's the most secure one, it looks so professinal and 'complete' and it offers everything an admin can desire. I'll give my pros and cons on the topic:

phpBB

Pros:
1. It's free.
2. You can code for it with ease.

Cons:
1. It offers the least functionality compared to its competitors.
2. Low level of security.

IPB

Pros:
1. Good for 'entertainment' sites.
2. Has some decent default functionality.
3. Coding is just a little bit more complicated that in phpBB, meaning - easy.
4. The IPB team is rarely trying to track nullified copies of their software(that's the reason it's very common for warez sites).

Cons:
1. Still has some security gaps.
2. For the sum of $160 you're expecting to see a MUCH more cleaner and organized code.

vBulletin Well...I love it.

Pros:
1. Very wide default functionality.
2. The best security a board can offer.
3. Very professional and very clean design and coding.
4. The leader in handling extremely(and i mean it!) large boards.

Cons:
1. It's definetely not free, but it's worth the money - $160(also has a leased license).
2. Difficult to code, requires advanced/expert PHP skills.
3. The vB team are like hounds when it comes to tracking nullified copies of their work, and have many agents doing it for them.

Well, this is my opinion (well defended I hope), so what's yours?