Among free and open source software, phpBB tops my list. Fairly good product, huge MOD database, and pretty good support.

If you haven't got much time, and want to see what the new phpbb3 can offer, just try it out on this host : <snipped>

Hope this can help!

Vbulletin is more Google SEO friendly, and you can have more visitors from google search results if you use Vbulletin

phpbb does struggle to get picked up properly by search bots I agree with that. Other forums with similar content does get picked quicker than a phpbb forum (in my experience)

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well just buy Vb and stick to only one forums rather than 3 else mybb is also better and free.
Don't just try to make 3 forums at a time its very hard to maintain forums.just stick to one first.

What about invision? I did an extensive look into which forums to use for a large online community I run..

In the end I chose iPB because of the support, mods available and plugins available..

I understand no one has written in this thread for like 2 weeks, but I feel I have something to add here. I do not reccomend SMF. I run SMF for my clan forums, and I will be the first one to tell you, there are A LOT(!!!) of exploits for SMF.

Go with Vbulletin it simply the safest if you keep updatin' it and add the patchs from the support site, vB gives your user alot of interactive which helps to make it more friendly and nice

i heard somewhere that Vbulletin is better In SEO and SERP

Exactly on point - there is no way to predict time tables exactly with a new site - let alone a new Forum. The technical choice is less critical in a Forum - than figuring out how you will grow & manage it.

I think phpBB is a little clunky and aged - hard to really change styles with - but you can get everything you need. SMF is more modern but still slightly smaller community and missing 1 or two things.

vBulletin is fine & dandy - but you can't modify source if you need or want to - or are into extensions - or want to do CMS at same time you depend on plug ins.

There is no one right answer to the software question - as it depends on you - but Dani is right - your time frames are WAY out of whack...

Just saw some one here posted link to http://www.forummatrix.org/ liked the site where you can compare different forums Also i agree with Dani. Dont run after 3 balls when you cant even catch one.