Hey tado, the mybb board software looks pretty good. I like the general look much better than phpbb - looks like a great alternative. Of course, it still has things that paid software doesn't have, but it looks good.
It all depends on what you want and how much you're willing to pay.
Vbulletin is liscenced, and I hate it for that. If you buy a liscence you have to renew it or your forum will shut down - when contrasted, Invision software you must buy a liscence as well, but you can still use the software.
Personally, I preffer phpbb because it's free. Easy to use and customize, but obviouisly, if you pay money, you're going to get more and better features. Phpbb is generally better for beginners, but it depends on taste.
vBulletin. Thats what all of the biggest forums online use, so there must be something good about it! They have amazing support and so many great skins to choose from.